Port upstream table escaped pipe fix

[Renakoni]

Summary

• Port upstream MarkText PR #4850 into the Android Muya copy.
• Fix escaped pipes inside table-cell inline code so the editor displays | / || instead of \| / \|\|.
• Add regression coverage for editor rendering, table structure, and markdown round-trip behavior.

Upstream Source

• Upstream PR: fix(muya): show escaped pipe in table cell code as | not \| (#4849) marktext/marktext#4850
• Upstream issue: [Bug] marktext/marktext#4849

Android Relevance

This directly affects Android's live Muya editor rendering. GFM table cells escape literal pipes as \|; after parsing, that escape should be stored as a literal pipe. The previous import path re-added \| into the stored table-cell text. That looked acceptable in plain cell text because the inline escape rule hides the backslash, but inside inline code the backslash is literal, so Android users saw code cells like \| instead of |.

Change Details

• Remove table-cell import-time re-escaping from MarkdownToState.
• Store table-cell text as marked emits it, with \| already resolved to literal |.
• Keep round-trip behavior through the existing stateToMarkdown.escapeText serialization path, which re-escapes pipes when writing markdown.
• Add tableEscapedPipe.spec.ts covering:
  • editor code rendering for `\|` and `\|\|`;
  • table row/cell structure preservation;
  • serialization round-trip for inline-code and plain-text escaped pipes.

Verification

• pnpm --dir third_party/muya exec vitest run src/state/__tests__/tableEscapedPipe.spec.ts passed.
• pnpm build passed.