Additional relations support for CompositeID models

[gwynne]

This update includes the following:

• Model.joined(_:) now works correctly with both aliased models and models with spaces.
• Lots more documentation comments in various places.
• DatabaseInput got a new flag to allow explicitly requesting that all properties - not just modified ones - be included. See the inline documentation for more details. All built-in FluentKit property types appropriately respect this flag.
• Fix completely incorrect implementation of KeyPrefixingStrategy's .camelCase strategy, including adding unit tests.
• Removed outdated checks for Swift version and OS minimums in Concurrency support since we require those minimums already.
• @Group properties with unset values no longer crash when encoded.
• @CompositeID properties can now be encoded/decoded even when explicitly given nil value.
• Implemented @CompositeOptionalParent, @CompositeChildren, and @CompositeOptionalChild properties to go with @CompositeParent, all of which allow fully describing relations even when the parent side of the relationship has a composite ID.
• The minimum Swift version requirement has been bumped from 5.5 to 5.5.2. The recommended minimum version is 5.6.

[codecov-commenter]

Codecov Report

Merging #550 (ee3d51e) into main (10f3213) will increase coverage by 1.66%. The diff coverage is 49.04%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #550 +/- ## ========================================== + Coverage 45.66% 47.33% +1.66% ========================================== Files 103 106 +3 Lines 5847 6180 +333 ========================================== + Hits 2670 2925 +255 - Misses 3177 3255 +78 ``` | Flag | Coverage Δ | | |---|---|---| | unittests | `47.33% <49.04%> (+1.66%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#carryforward-flags-in-the-pull-request-comment) to find out more. | [Impacted Files](https://codecov.io/gh/vapor/fluent-kit/pull/550?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor) | Coverage Δ | | |---|---|---| | [Sources/FluentKit/Concurrency/AsyncMigration.swift](https://codecov.io/gh/vapor/fluent-kit/pull/550?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9GbHVlbnRLaXQvQ29uY3VycmVuY3kvQXN5bmNNaWdyYXRpb24uc3dpZnQ=) | `0.00% <ø> (ø)` | | | [...s/FluentKit/Concurrency/AsyncModelMiddleware.swift](https://codecov.io/gh/vapor/fluent-kit/pull/550?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9GbHVlbnRLaXQvQ29uY3VycmVuY3kvQXN5bmNNb2RlbE1pZGRsZXdhcmUuc3dpZnQ=) | `0.00% <ø> (ø)` | | | [...s/FluentKit/Concurrency/Children+Concurrency.swift](https://codecov.io/gh/vapor/fluent-kit/pull/550?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9GbHVlbnRLaXQvQ29uY3VycmVuY3kvQ2hpbGRyZW4rQ29uY3VycmVuY3kuc3dpZnQ=) | `0.00% <0.00%> (ø)` | | | [...s/FluentKit/Concurrency/Database+Concurrency.swift](https://codecov.io/gh/vapor/fluent-kit/pull/550?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9GbHVlbnRLaXQvQ29uY3VycmVuY3kvRGF0YWJhc2UrQ29uY3VycmVuY3kuc3dpZnQ=) | `0.00% <ø> (ø)` | | | [...luentKit/Concurrency/EnumBuilder+Concurrency.swift](https://codecov.io/gh/vapor/fluent-kit/pull/550?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9GbHVlbnRLaXQvQ29uY3VycmVuY3kvRW51bUJ1aWxkZXIrQ29uY3VycmVuY3kuc3dpZnQ=) | `0.00% <ø> (ø)` | | | [...rces/FluentKit/Concurrency/Model+Concurrency.swift](https://codecov.io/gh/vapor/fluent-kit/pull/550?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9GbHVlbnRLaXQvQ29uY3VycmVuY3kvTW9kZWwrQ29uY3VycmVuY3kuc3dpZnQ=) | `25.00% <ø> (ø)` | | | [...ntKit/Concurrency/ModelResponder+Concurrency.swift](https://codecov.io/gh/vapor/fluent-kit/pull/550?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9GbHVlbnRLaXQvQ29uY3VycmVuY3kvTW9kZWxSZXNwb25kZXIrQ29uY3VycmVuY3kuc3dpZnQ=) | `0.00% <ø> (ø)` | | | [...entKit/Concurrency/OptionalChild+Concurrency.swift](https://codecov.io/gh/vapor/fluent-kit/pull/550?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9GbHVlbnRLaXQvQ29uY3VycmVuY3kvT3B0aW9uYWxDaGlsZCtDb25jdXJyZW5jeS5zd2lmdA==) | `0.00% <0.00%> (ø)` | | | [...ntKit/Concurrency/OptionalParent+Concurrency.swift](https://codecov.io/gh/vapor/fluent-kit/pull/550?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9GbHVlbnRLaXQvQ29uY3VycmVuY3kvT3B0aW9uYWxQYXJlbnQrQ29uY3VycmVuY3kuc3dpZnQ=) | `0.00% <0.00%> (ø)` | | | [...ces/FluentKit/Concurrency/Parent+Concurrency.swift](https://codecov.io/gh/vapor/fluent-kit/pull/550?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9GbHVlbnRLaXQvQ29uY3VycmVuY3kvUGFyZW50K0NvbmN1cnJlbmN5LnN3aWZ0) | `0.00% <0.00%> (ø)` | | | ... and [30 more](https://codecov.io/gh/vapor/fluent-kit/pull/550?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor) | |

[gwynne]

API breakage check remarks:

• Changes to the "public" types in FluentBenchmark are not true API breakage; only the top-level test methods should be invoked by dependents.
• The new protocol requirement in DatabaseInput has a public default implementation and does not require any changes by external code.

[VaporBot]

These changes are now available in 1.39.0