5/7: DOM scripting engine & currentColor hardening

[Amnell]

Summary

Implement a JavaScript DOM scripting engine for SVG DOM manipulation tests, plus comprehensive currentColor inheritance hardening and test controls.

Changes

DOM Scripting Engine:

• Implement coords-dom-01-f and coords-dom-02-f
• Begin script support (ScriptRunner)
• Implement stroke and fill support in scripting engine
• Implement stroke-dasharray and stroke-dashoffset
• Implement linecap, linejoin and miterlimit
• Add fill-rule support in ScriptRunner
• Add currentColor support in ScriptRunner
• Implement coords-dom-03-f and coords-dom-04-f

currentColor Hardening:

• Harden currentColor inheritance and override precedence
• Add runtime behavior and regression controls
• Add text/stroke currentColor parity and relink controls
• Add mixed-node inheritance, style source precedence controls
• Add opacity hardening, mutation ordering, clamping controls
• Add invalid color/opacity, edge token, malformed token controls
• Add function-notation and CSS-wide keyword controls

Misc:

• Gitignore .vscode

Merge order

⚠️ Merge these PRs in order: #8 → #9 → #10 → #11 → #12 → #13 → #14. After merging each PR, GitHub will automatically update the next PR's base to main.

Stack:

1. Swift 6 prep & test modernization (1/7: Swift 6 prep & test modernization #8)
2. Docs & tooling (2/7: Project docs, tooling & initial W3C coverage #9)
3. Pattern/gradient paint servers (3/7: Implement pattern & gradient paint servers #10)
4. Test reporting (4/7: HTML test report generation #11)
5. DOM scripting & currentColor ← this PR
6. Shapes & coordinates
7. Structural elements & text