Port text rendering from ttf-parser to skrifa

This replaces ttf-parser with skrifa for all font parsing and text rendering.

fontdb changes:
- Vendor fontdb 0.23.0 as a workspace crate
- Replace ttf-parser with skrifa for font parsing
- Use skrifa's MetadataProvider for font attributes and metrics

usvg changes:
- Add skrifa_colr.rs: COLR glyph painting using skrifa's ColorPainter
- Add skrifa_metrics.rs: Font metrics extraction using skrifa
- Update flatten.rs: Use skrifa for glyph outlines and bitmap extraction
- Update layout.rs: Use skrifa for font metrics and harfrust for shaping
- Replace rustybuzz with harfrust for text shaping
- Update test reference images for new skrifa-based rendering

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: oetiker

.github/copyright.sh

@@ -7,7 +7,8 @@
 #   -g "!src/special_directory"
 
 # Check all the standard Rust source files
-output=$(rg "^// Copyright (19|20)[\d]{2} (.+ and )?the Resvg Authors( and .+)?$\n^// SPDX-License-Identifier: Apache-2\.0 OR MIT$\n\n" --files-without-match --multiline -g "*.{rs,c,cpp,h}" .)
+# Exclude vendored fontdb (has its own copyright from original author)
+output=$(rg "^// Copyright (19|20)[\d]{2} (.+ and )?the Resvg Authors( and .+)?$\n^// SPDX-License-Identifier: Apache-2\.0 OR MIT$\n\n" --files-without-match --multiline -g "*.{rs,c,cpp,h}" -g "!crates/fontdb/*" .)
 
 if [ -n "$output" ]; then
 	echo -e "The following files lack the correct copyright header:\n"

Cargo.lock

@@ -1,6 +1,7 @@
 [workspace]
 members = [
     "crates/c-api",
+    "crates/fontdb",
     "crates/resvg",
     "crates/usvg",
     "crates/usvg/codegen",

Cargo.toml

@@ -0,0 +1,34 @@
+[package]
+name = "fontdb"
+version = "0.23.0"
+authors = ["Yevhenii Reizner <[email protected]>"]
+edition = "2024"
+rust-version = "1.87.0"
+license = "MIT"
+description = "A simple, in-memory font database with CSS-like queries. Vendored for resvg with skrifa backend."
+repository = "https://github.com/linebender/resvg"
+documentation = "https://docs.rs/fontdb/"
+keywords = ["font", "db", "css", "truetype", "opentype"]
+categories = ["text-processing"]
+
+[dependencies]
+slotmap = "1.0"
+tinyvec = { version = "1.8", features = ["alloc"] }
+skrifa = "0.40"
+log = "0.4"
+
+memmap2 = { version = "0.9", optional = true }
+fontconfig-parser = { version = "0.5.8", optional = true }
+
+[features]
+default = ["std", "fs", "system-fonts", "memmap"]
+# Enables standard library support (always on for this vendored version).
+std = []
+# Enables file system operations (loading fonts from files/directories).
+fs = ["std"]
+# Enables system fonts loading.
+system-fonts = ["fs", "fontconfig"]
+# Enables fontconfig support on Linux.
+fontconfig = ["fontconfig-parser"]
+# Enables font files memory mapping for faster loading.
+memmap = ["fs", "memmap2"]