fix(editor-ext): remove duplicate escapeHtmlAttr (TS2393, broken CI)

Merging the image-captions (#221) and lossless-export branches each added
its own escapeHtmlAttr in turndown.utils.ts, producing two implementations
of the same function and breaking `tsc --build` (TS2393) — which failed the
Build editor-ext step across all CI jobs.

Drop the lighter image-captions duplicate (escapes & and ") and keep the
fuller version (escapes & " < >). It is a strict superset: both call sites
(serializeAttrs, the image rule) place the value inside a double-quoted HTML
attribute, where extra < > escaping is harmless and idempotent on re-import.
Verified: editor-ext builds; turndown.dataloss + image-markdown tests pass.

packages/editor-ext/src/lib/markdown/utils/turndown.utils.ts

@@ -12,14 +12,6 @@ function sanitizeMdLinkText(value: string): string {
     .replace(/[\r\n]+/g, ' ');
 }
 
-// Escape a value placed inside a double-quoted HTML attribute (img src/alt/
-// data-caption in the raw-HTML image fallback). Only & and " are special in
-// that context; escaping them is idempotent because parse5/marked decode them
-// back on re-import.
-function escapeHtmlAttr(value: string): string {
-  return value.replace(/&/g, '&').replace(/"/g, '"');
-}
-
 // Tags turndown treats as void (self-closing). Footnote references render as an
 // empty <sup data-footnote-ref> whose meaning lives entirely in its data-id;
 // without marking it void, turndown's blank-node removal drops it before our