Speed up svg parsing and rendering

[kunitoki]

This pull request introduces significant optimizations and refactorings to the SVG and core text modules, primarily aimed at improving performance and maintainability. The most notable changes are the pre-resolution of gradient and filter references at parse time (avoiding repeated resolution during rendering), the introduction of a hash generator utility for efficient hashing, and the implementation of a fast CSS rule index for SVG parsing. Additionally, blend mode parsing has been simplified and made more robust, and some hot code paths have been optimized to reduce unnecessary allocations.

SVG Parsing and Rendering Optimizations:

• Gradients and filters are now fully resolved at parse time, eliminating the need for repeated resolution during rendering. This involves traversing href chains for gradients and filters once and updating their lookup tables accordingly. (modules/yup_graphics/svg/yup_SVGParser.cpp [1] [2]
• The resolveGradient and resolveFilter functions and their usages have been removed from the rendering code, as resolution is now handled during parsing. (modules/yup_graphics/drawables/yup_Drawable.cpp [1] [2] [3] [4]

CSS Rule Matching Improvements:

• Introduced SVGCssRuleIndex, a new structure for fast lookup of CSS rules by tag, id, and class, and integrated it into the SVG CSS parser. This replaces brute-force matching and greatly improves stylesheet application performance. (modules/yup_graphics/svg/yup_SVGCssRule.h [1] modules/yup_graphics/svg/yup_SVGCssParser.h [2] modules/yup_graphics/svg/yup_SVGParser.cpp [3]

Hashing Infrastructure Improvements:

• Extracted and documented a generic HashGenerator utility for use throughout the codebase, improving code reuse and maintainability. This is now used for hashing in both String and StringRef. (modules/yup_core/misc/yup_HashGenerator.h [1] modules/yup_core/text/yup_String.cpp [2] modules/yup_core/text/yup_StringRef.h [3] modules/yup_core/yup_core.h [4]
• Added a hash function for StringRef in the default hash functions to enable its use as a key in hash maps. (modules/yup_core/containers/yup_HashMap.h [1] [2]

Blend Mode and Attribute Parsing Simplification:

• Replaced long chains of conditional statements for blend mode parsing with a single utility function, making the code more concise and easier to maintain. (modules/yup_graphics/svg/yup_SVGParser.cpp [1] [2]
• Optimized the SVG unit parsing function to avoid unnecessary string allocations, improving performance in a hot code path. (modules/yup_graphics/svg/yup_SVGParser.cpp modules/yup_graphics/svg/yup_SVGParser.cppL2060-R2014)

[codecov]

Codecov Report

❌ Patch coverage is 98.47095% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.73%. Comparing base (3167a0c) to head (ec4cd97).

Files with missing lines	Patch %	Lines
modules/yup_graphics/svg/yup_SVGCssParser.cpp	98.70%	3 Missing ⚠️
modules/yup_graphics/svg/yup_SVGParser.cpp	96.82%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #170      +/-   ##
==========================================
+ Coverage   80.58%   80.73%   +0.15%     
==========================================
  Files         777      779       +2     
  Lines       80278    80246      -32     
==========================================
+ Hits        64689    64786      +97     
+ Misses      15589    15460     -129     

Files with missing lines	Coverage Δ
modules/yup_core/containers/yup_HashMap.h	98.36% <100.00%> (+<0.01%)	⬆️
modules/yup_core/misc/yup_HashGenerator.h	100.00% <100.00%> (ø)
modules/yup_core/text/yup_String.cpp	96.92% <ø> (-0.02%)	⬇️
modules/yup_core/text/yup_StringRef.h	86.66% <100.00%> (+0.95%)	⬆️
modules/yup_graphics/drawables/yup_Drawable.cpp	77.91% <100.00%> (-0.25%)	⬇️
modules/yup_graphics/svg/yup_SVGCssRule.h	100.00% <100.00%> (ø)
modules/yup_graphics/svg/yup_SVGParser.cpp	89.60% <96.82%> (+7.72%)	⬆️
modules/yup_graphics/svg/yup_SVGCssParser.cpp	98.62% <98.70%> (-1.01%)	⬇️

... and 5 files with indirect coverage changes

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