Add emoji support to SpriteText and TextBox

[EYHN]

This PR continues the work of @Susko3 in #5933, introducing comprehensive Unicode text handling improvements and colored font support. @Susko3's commits are already included in this PR, so only this PR needs to be merged.

I believe this PR is now ready for review. I've attempted to solve most of the major issues, including support for multi-codepoint emoji for flags and TextBox support for emoji. To achieve this, I introduced a new Grapheme structure to replace Rune, and generated emoji resources from noto color emoji. Those changes that I think warrant discussion, so please share your thoughts.

If you want to test the game yourself, please switch to https://github.com/EYHN/osu/tree/eyhn/emoji and use the local framework and resource from ppy/osu-resources#369

---

This fully emoji support feature is divided into three PRs.

• In osu Add full Emoji support to osu osu#34012
• In osu-framework (This PR)
• In osu-resources Add noto color emoji osu-resources#369

Grapheme Implementation

I introduced the Grapheme struct to represent a single grapheme cluster in Unicode text, efficiently handling both simple char and complex multi-character sequences (like emoji with skin tone modifiers, flags, or characters with combining marks).

The key differences from existing types are:

• char: Represents a single UTF-16 code unit, insufficient for complex Unicode characters
• Rune: Represents a Unicode scalar value, but doesn't handle grapheme clusters
• Grapheme: Represents complete user-perceived characters, including complex clusters

I optimized the Grapheme struct's memory allocation by using direct char storage for common characters and string storage only for complex graphemes, resulting in minimal heap allocations and negligible performance impact.

Performance benchmarks show that using Grapheme instead of char actually improves performance:

Using char (original):

Method	Mean	Error	StdDev
AddCharacters	149.2 μs	1.98 μs	1.85 μs
AddCharactersWithDifferentBaselines	151.9 μs	2.26 μs	2.00 μs
RemoveLastCharacter	148.0 μs	2.20 μs	1.84 μs
RemoveLastCharacterWithDifferentBaselines	161.2 μs	3.21 μs	3.30 μs
AddText	371.1 μs	7.06 μs	8.13 μs

Using Grapheme:

Method	Mean	Error	StdDev
AddCharacters	140.3 μs	1.11 μs	1.04 μs
AddCharactersWithDifferentBaselines	142.4 μs	1.00 μs	0.88 μs
RemoveLastCharacter	141.1 μs	0.55 μs	0.52 μs
RemoveLastCharacterWithDifferentBaselines	143.5 μs	0.56 μs	0.52 μs
AddText	340.2 μs	3.27 μs	2.90 μs

Colored Font Rendering

I added a Coloured property to ITexturedCharacterGlyph. When Coloured == true:

• Colored font textures are created
• SpriteText skips tinting during rendering to preserve original colors

TextBox Emoji Support

I refactored TextBox to work with Grapheme instead of string indices. The component now maintains dual state: string text and List<Grapheme> graphemes. I changed nearly all position-based variables to use grapheme positions, ensuring proper handling of complex Unicode characters in text input.

Recording.2025-06-26.134618.mp4

Noto Color Emoji Resources

Resources: Available in ppy/osu-resources#369

[bdach]

so is #5933 a prerequisite of this PR or not? because it's very unclear. like you've massacred the history here, it appears you squashed the entirety of that PR into e2f8661? that's not how you're supposed to do any of this

[EYHN]

@bdach Yes, #5933 is already included in this PR.

When i ready for review, I will reorganize the history.