refactor: replace bcp-47-normalize with lightweight BCP-47 normalization (-185 KB)

[PascalThuet]

Summary

• Remove bcp-47-normalize dependency and its transitive deps (bcp-47, is-alphabetical, is-alphanumerical, is-decimal)
• Replace with a ~75-line internal utility src/streaming/utils/BCP47Utils.js
• -185,508 bytes on dash.all.min.js (-18.9%)

What changed

New file: src/streaming/utils/BCP47Utils.js

• normalizeBcp47(tag): RFC 5646 case normalization (language → lowercase, script → titlecase, region → uppercase) + complete ISO 639-2/B and 639-2/T → ISO 639-1 lookup table (184 entries)

Modified files: replaced import {bcp47Normalize} from 'bcp-47-normalize' with import {normalizeBcp47} from '...BCP47Utils.js' in:

• src/streaming/controllers/MediaController.js (2 call sites)
• src/dash/parser/matchers/LangMatcher.js (1 call site)
• src/dash/DashAdapter.js (1 call site)

package.json: removed bcp-47-normalize from dependencies. bcp-47-match (provides extendedFilter()) is unchanged.

Bundle size

Measured on development branch (v5.2.0), modern prod build:

	Before	After	Diff
dash.all.min.js	983,658 B	798,150 B	-185,508 B (-18.9%)
dash.all.debug.js	3,503,300 B	3,245,971 B	-257,329 B (-7.3%)

What is NOT covered

The full bcp-47-normalize also handles features dash.js never uses:

• Deprecated language aliases (iw → he, in → id): rare in real MPDs. A small table could be added later if needed.
• Likely subtag expansion (zh → zh-Hans-CN): unnecessary because extendedFilter() already matches via RFC 4647 prefix matching.

Test plan

• All 3,332 unit tests pass without modification
• Tests exercising ISO 639-2 codes pass (spa → es, fre → fr)
• Manual: VOD playback with audio language selection
• Manual: Content with CEA-608 captions

Fixes #4969

[Copilot]

Pull request overview

This PR removes the heavyweight bcp-47-normalize dependency and replaces it with a small internal BCP-47 normalization utility to reduce the shipped bundle size, while keeping the language-tag normalization behavior needed by dash.js.

Changes:

• Added normalizeBcp47() utility with RFC 5646 case normalization + ISO 639-2 → 639-1 mapping.
• Updated DASH parsing/selection code paths to use normalizeBcp47() instead of bcp47Normalize().
• Removed bcp-47-normalize from package.json dependencies.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/streaming/utils/BCP47Utils.js	Introduces internal BCP-47 normalization + ISO 639-2→1 mapping table.
src/streaming/controllers/MediaController.js	Switches language matching normalization to the new internal utility.
src/dash/parser/matchers/LangMatcher.js	Switches MPD lang attribute normalization to the new internal utility.
src/dash/DashAdapter.js	Switches CEA-608 caption language normalization to the new internal utility.
package.json	Removes the bcp-47-normalize dependency entry.

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