refactor(ast): migrate JavaScript string values to JSStr - #26548

Decoded JavaScript strings currently use UTF-8 text plus separate lone-surrogate flags. Consumers can lose those flags or treat the internal escape encoding as literal text when constructing a new value.

Carry JSStr through decoded AST values, module requests, and their consumers, building on #26435. This is a Rust API change: callers that need UTF-8 must handle JSStr::as_str() returning None. Raw source text and identifiers keep their UTF-8 types. The draft includes enum evaluation and the associated owned UTF-16 storage; it does not introduce a general owned JSString.

Suggested review order

1. Representation and parsing: AST string/cooked fields, lexer escape decoding, and parser recovery. Check that raw text stays distinct from decoded values and that surrogate pairs normalize across append boundaries.
2. Output boundaries: oxc_str serialization, codegen, module-record conversion, and NAPI. Check JSON, raw-transfer, and lazy-transfer behavior, especially the Option<JSStr> niche and layout assertions.
3. Enum evaluation: review the UTF-8/UTF-16 constant variants, surrogate-name hash table, scope separation, and cloning as one area.
4. Other consumers: most linter edits adapt comparisons or explicitly reject values that UTF-8-only analysis cannot represent. String reconstruction, minifier folding, and JSX entity decoding need closer review than mechanical type updates.
5. Generated output and regressions: read the generators before the generated diff. The js-str.test.ts files in the parser, minifier, and transformer bindings cover string values, module requests, recovery, and runtime behavior.

Deferred to a follow-up: simplify EscapeTable / StandardEscapeTable in oxc_estree into direct helpers. The migration retains their existing structure and eight-byte escape scanner while removing the obsolete marker decoder.

just ready passed after the latest commit, including workspace tests, Clippy, documentation, formatting, and generated-file checks; the working tree is clean. Additional validation covered parser conformance (no new failures), native parser/minifier/transformer tests, 3,723 runtime checks, and size/allocation tracking. Minifier size snapshots are unchanged. JavaScript lint and all 61 transformer binding tests also passed, and scalar lexer conformance regenerated only the expected fixture count. A direct Node/WASI smoke check covered module dependencies and enum string values. Browser execution has not been validated locally.

Part of #26242.

Implemented with AI assistance; draft for human review.