refactor(reflection): no longer fallback to anonymous types automatically

[RiscadoA]

Description

This change was necessary due to the previous system being highly error prone. Before, if reflect was called for a type T without defined reflection included, a placeholder definition would be used which returned an anonymous type. Sadly, due to the C++ One Definition Rule, this meant that other source files using reflect, could return an anonymous type, even if the type's reflection definition was included!

Basically, previously a simple mistake such as forgetting to include an external reflection header could lead to a random reflection failure in the core of the library, such as a missing trait error. Now, the users must define reflection for all types, as there is no longer a fallback. To simplify this for the previous 'anonymous types', a new CUBOS_ANONYMOUS_REFLECT macro was added.

Checklist

• [x] Self-review changes.
• [x] Evaluate impact on the documentation.
• [x] Ensure test coverage.
• [x] Write new samples.
• [x] Add entry to the changelog's unreleased section.

[github-actions[bot]]

PR Preview Action v1.4.7 :---: :rocket: Deployed preview to https://GameDevTecnico.github.io/cubos/preview/pr-1289/ on branch gh-pages at 2024-08-02 08:03 UTC

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 69.23077% with 12 lines in your changes missing coverage. Please review.

Project coverage is 36.26%. Comparing base (fedd0bf) to head (9392e47).

Files	Patch %	Lines
core/src/reflection/reflect.cpp	88.88%	2 Missing :warning:
engine/src/physics/fixed_substep/plugin.cpp	0.00%	1 Missing :warning:
engine/src/render/bloom/plugin.cpp	0.00%	1 Missing :warning:
engine/src/render/deferred_shading/plugin.cpp	0.00%	1 Missing :warning:
engine/src/render/g_buffer_rasterizer/plugin.cpp	0.00%	1 Missing :warning:
engine/src/render/mesh/plugin.cpp	0.00%	1 Missing :warning:
engine/src/render/ssao/plugin.cpp	0.00%	1 Missing :warning:
engine/src/render/tone_mapping/plugin.cpp	0.00%	1 Missing :warning:
engine/src/ui/canvas/plugin.cpp	0.00%	1 Missing :warning:
engine/src/ui/color_rect/plugin.cpp	0.00%	1 Missing :warning:
... and 1 more

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1289 +/- ## ========================================== - Coverage 36.27% 36.26% -0.01% ========================================== Files 376 376 Lines 30851 30864 +13 ========================================== + Hits 11191 11194 +3 - Misses 19660 19670 +10 ```

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