refactor: Remove custom targets, use 'None' item group

[jviau]

Description

This PR refactors the python worker nuget package targets as follows:

1. Removes current custom targets/properties
   1. Properties, items, targets all share the same global namespace. Naming these generally increases risk of conflicts with other props/items/targets.
2. Leverages None item group with appropriate metadata to have CopyToOutputDirectory and CopyToPublishDirectory targets perform the copies for us.
   1. Instead of copying files to output or publish manually, you can add to various existing item groups and tag them to be copied.
   2. This change improves incremental build support, avoiding copies when the files already exist at the destination.
3. Adds additional logic to copy only specific runtime files with a runtime identifier is specified.
   1. Will error out if the runtime identifier is not supported.

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PR information

• [x] The title of the PR is clear and informative.
• [x] There are a small number of commits, each of which has an informative message. This means that previously merged commits do not appear in the history of the PR. For information on cleaning up the commits in your pull request, see this page.
• [ ] If applicable, the PR references the bug/issue that it fixes in the description.
• [ ] New Unit tests were added for the changes made and CI is passing.

Quality of Code and Contribution Guidelines

• [x] I have read the contribution guidelines.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 45.88%. Comparing base (c244569) to head (2f40dbd). Report is 3 commits behind head on dev.

:exclamation: Current head 2f40dbd differs from pull request most recent head 6586aaf

Please upload reports for the commit 6586aaf to get more accurate results.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev #1472 +/- ## =========================================== - Coverage 83.03% 45.88% -37.15% =========================================== Files 36 35 -1 Lines 2322 2040 -282 Branches 346 302 -44 =========================================== - Hits 1928 936 -992 - Misses 295 1028 +733 + Partials 99 76 -23 ``` | [Flag](https://app.codecov.io/gh/Azure/azure-functions-python-worker/pull/1472/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Azure) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/Azure/azure-functions-python-worker/pull/1472/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Azure) | `45.88% <ø> (-37.15%)` | :arrow_down: | 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=Azure#carryforward-flags-in-the-pull-request-comment) to find out more.

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