Create MVP of <filter> effect sufficient for the Donner splash screen

[jwmcglynn]

This makes progress towards #151, adding the following functionality:

• <filter> element support with minimal attributes
• <feGaussianBlur> element support with minimal attributes
• Basic filter presentation attribute support, sufficient to support blur and element references.

This also refactors the component model, and introduces a separate System concept to separate the component data model from logic. Lots of doxygen documentation has also been added.

What filter support remains?

• [ ] Support for filter effect chains, right now it is bounded to a single primitive.
• [ ] Support for the various <filter> and filter primitive attributes, such as the bounding box and filterUnits
• [ ] Support for converting CSS lengths into user units, as CSS filters can include units, for example filter: blur(5in)

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 76.26648% with 342 lines in your changes are missing coverage. Please review.

Project coverage is 87.53%. Comparing base (9952a68) to head (1df398c).

Files	Patch %	Lines
src/svg/components/shadow/shadow_tree_system.cc	56.73%	54 Missing and 7 partials :warning:
src/svg/properties/property_registry.cc	23.63%	38 Missing and 4 partials :warning:
src/svg/components/shape/shape_system.cc	82.58%	25 Missing and 10 partials :warning:
...rc/svg/svg_filter_primitive_standard_attributes.cc	12.82%	34 Missing :warning:
src/svg/xml/attribute_parser.cc	62.50%	20 Missing and 10 partials :warning:
src/svg/components/paint/paint_system.cc	84.43%	20 Missing and 6 partials :warning:
src/svg/components/filter/filter_effect.cc	0.00%	17 Missing :warning:
src/svg/renderer/renderer_skia.cc	82.25%	7 Missing and 4 partials :warning:
src/svg/components/rendering_context.cc	80.43%	7 Missing and 2 partials :warning:
src/svg/components/style/style_system.cc	81.63%	8 Missing and 1 partial :warning:
... and 21 more

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #162 +/- ## ========================================== - Coverage 88.09% 87.53% -0.57% ========================================== Files 230 243 +13 Lines 17647 18167 +520 Branches 2002 2044 +42 ========================================== + Hits 15547 15902 +355 - Misses 1518 1667 +149 - Partials 582 598 +16 ``` | [Flag](https://app.codecov.io/gh/jwmcglynn/donner/pull/162/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jeff+McGlynn) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/jwmcglynn/donner/pull/162/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jeff+McGlynn) | `87.52% <76.26%> (-0.58%)` | :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=Jeff+McGlynn#carryforward-flags-in-the-pull-request-comment) to find out more.

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