LT-22638: Show OpenType feature names and multi-valued variants

[jasonleenaylor]

Summary

Fixes LT-22638. Makes OpenType font
features usable in Font Options: features show human-readable names from the
font (or a registered-feature catalog), and character variants with multiple
named alternates are selectable instead of a single On/Off toggle — parity with
the existing Graphite experience, with no change to the dropdown menu, so both
the Writing System and Styles font dialogs inherit it.

What changed

• New OpenTypeFontFeatureInfoReader (FwUtils) — parses GSUB/GPOS feature
  lists, featureParams, and the name table via a table-source delegate (GDI
  GetFontData in the app, font-file bytes in tests). Bounds-checked; malformed
  fonts degrade to tag-only records. Adapted from Paratext's OpenTypeFeatures.Ttf.
• New OpenTypeFeatureCatalog (FwUtils) — classifies registered features
  (hidden / default-on) and supplies English names, seeded from Paratext and
  audited against the OpenType registry (dlig visible, aalt hidden, kern
  default-on).
• Rewrote the OpenType provider in FontFeaturesButton — character variants
  with named options become "None + option" submenus stored as cvNN=k; labels
  resolve font-supplied → resx → catalog → numbered fallback; default-on features
  initialize enabled; hidden features filtered.
• resx — added None / numbered-set fallbacks; removed dead labels (aalt,
  ccmp) and entries orphaned by the rewrite (ss01–ss05, ValueOff/ValueOn).
• Docs — Docs/opentype-font-features.md updated.

Storage, rendering, and CSS/Word export are untouched — the renderer-neutral
tag=value string already carried multi-values.

Testing

• Reader verified against real Charis SIL 6.200 (cv43 "Capital Eng" + 3
  options, ss01 "Single-story a and g", GPOS mark/mkmk) and Scheherazade
  New (cv70 "Damma").
• Synthetic malformed-table robustness tests.
• Provider tests: multi-value cv, binary fallback, default-on init, label
  priority, hidden filtering, cv43=2 round-trip, resx↔catalog consistency.
• Green: FwUtilsTests 33, FwCoreDlgControlsTests 17, FwCoreDlgsTests 19. Coverage:
  catalog/info 100%, reader 86%.
• Manual acceptance passed (WS setup → Font tab → Charis → Font Features).

🤖 Generated with Claude Code

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This change is 

[github-actions]

NUnit Tests

    1 files  ± 0      1 suites  ±0   10m 51s ⏱️ + 2m 38s
4 345 tests +32  4 272 ✅ +32  73 💤 ±0  0 ❌ ±0 
4 354 runs  +32  4 281 ✅ +32  73 💤 ±0  0 ❌ ±0 

Results for commit b8a2dd1. ± Comparison against base commit ac89f08.

This pull request removes 2 and adds 34 tests. Note that renamed tests count towards both.

SIL.FieldWorks.FwCoreDlgControlsTests.TestFontFeaturesButton ‑ OpenTypeFontFeatureReader_CachesFeatureTagsForSameFontKey
SIL.FieldWorks.FwCoreDlgControlsTests.TestFontFeaturesButton ‑ OpenTypeFontFeatureReader_FiltersRequiredShapingFeatures

SIL.FieldWorks.Common.FwUtils.OpenTypeFeatureCatalogTests ‑ AccessAllAlternates_IsHidden
SIL.FieldWorks.Common.FwUtils.OpenTypeFeatureCatalogTests ‑ CommonlyDefaultOnFeatures_AreDefaultOn("calt")
SIL.FieldWorks.Common.FwUtils.OpenTypeFeatureCatalogTests ‑ CommonlyDefaultOnFeatures_AreDefaultOn("clig")
SIL.FieldWorks.Common.FwUtils.OpenTypeFeatureCatalogTests ‑ CommonlyDefaultOnFeatures_AreDefaultOn("kern")
SIL.FieldWorks.Common.FwUtils.OpenTypeFeatureCatalogTests ‑ CommonlyDefaultOnFeatures_AreDefaultOn("liga")
SIL.FieldWorks.Common.FwUtils.OpenTypeFeatureCatalogTests ‑ DiscretionaryLigatures_AreUserVisible
SIL.FieldWorks.Common.FwUtils.OpenTypeFeatureCatalogTests ‑ LegacyBlocklistTags_AreAllHidden
SIL.FieldWorks.Common.FwUtils.OpenTypeFeatureCatalogTests ‑ UnknownTag_IsNeitherKnownNorHidden
SIL.FieldWorks.Common.FwUtils.OpenTypeFeatureCatalogTests ‑ VisibleFeatures_HaveEnglishNames
SIL.FieldWorks.Common.FwUtils.OpenTypeFontFeatureInfoReaderRobustnessTests ‑ FeatureParamsOffsetPastTableEnd_YieldsTagWithoutLabel
…

[codecov-commenter]

Codecov Report

❌ Patch coverage is 89.02148% with 46 lines in your changes missing coverage. Please review.
✅ Project coverage is 33.09%. Comparing base (321ba87) to head (b8a2dd1).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...rc/Common/FwUtils/OpenTypeFontFeatureInfoReader.cs	81.46%	16 Missing and 17 partials ⚠️
...FwCoreDlgs/FwCoreDlgControls/FontFeaturesButton.cs	85.36%	3 Missing and 9 partials ⚠️
Src/Common/FwUtils/OpenTypeFeatureCatalog.cs	99.37%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1029      +/-   ##
==========================================
+ Coverage   33.02%   33.09%   +0.07%     
==========================================
  Files        1202     1204       +2     
  Lines      278232   278559     +327     
  Branches    37169    37226      +57     
==========================================
+ Hits        91880    92196     +316     
+ Misses     158502   158493       -9     
- Partials    27850    27870      +20     

Files with missing lines	Coverage Δ
Src/Common/FwUtils/OpenTypeFeatureCatalog.cs	99.37% <99.37%> (ø)
...FwCoreDlgs/FwCoreDlgControls/FontFeaturesButton.cs	62.85% <85.36%> (+2.17%)	⬆️
...rc/Common/FwUtils/OpenTypeFontFeatureInfoReader.cs	81.46% <81.46%> (ø)

... and 3 files with indirect coverage changes

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