Preserve literal dollars in case-converted search replacements

[Suzu (Suzu1Dev)]

Workspace Search reinterprets dollar sequences in case-converted captures as replacement syntax. Searching ^(foo.*)$ in foo$1 and replacing with \U$1 currently produces FOOfoo$1; this change produces FOO$1 in both the preview and the saved file.

Fixes #334709.

Collect the converted capture separately and escape its literal dollars before appending it to the replacement template. Other capture substitutions continue through the existing path. Add seven regression cases covering capture references, whole-match/prefix/suffix references, escaped dollars, named-reference text, and mixed converted/unconverted captures.

Related to #299365 and #326451, which handle $$ entered in the replacement field. That PR does not cover dollar sequences in case-converted captured text. This branch is based directly on main and does not depend on #334698.

Validation

On macOS arm64 with Node 24.18.0:

• All seven new regression cases fail on the unmodified implementation and pass with this change.
• 258 related Electron unit tests pass; three existing/platform-specific tests are skipped.
• Changed-file ESLint, hygiene, and git diff --check pass.
• With fresh profiles and --disable-extensions, verified the Search view preview and actual Replace All edits in both baseline and fixed Code OSS: foo$1, foo$&, and foo$$ now become FOO$1, FOO$&, and FOO$$.

scripts/test.sh --runGlob 'vs/{workbench/services/search,workbench/contrib/search,editor/contrib/find}/test/**/*.test.js'
npm run eslint -- src/vs/workbench/services/search/common/replace.ts src/vs/workbench/services/search/test/common/replace.test.ts
npm run precommit -- src/vs/workbench/services/search/common/replace.ts src/vs/workbench/services/search/test/common/replace.test.ts

Refreshed the two changed JavaScript outputs using esbuild with the repository's transpile settings and reused the existing complete build. Full typecheck, full rebuild, and Windows/Linux validation were not rerun for this change.

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