Give YAML number/bool/null plain scalars a string-scalar ancestor

A typed plain scalar (`42`, `true`, `null`) is first an unquoted plain scalar —
lexically a string — that the schema then resolves to a number / boolean / null.
It was scoped as a flat `constant.numeric` / `constant.language`, missing the
`string.unquoted` ancestor the official grammar carries (`string.unquoted.plain.out`
› `constant.*`).

That ancestor is load-bearing for folding: when a value scalar is continued by a
more-indented line (`: null\n  d`) the value is actually the multi-line plain
string "null d", but a highlighter cannot see the continuation while scoping the
first line. The `string.unquoted` ancestor keeps it string-typed regardless, while
a standalone `null` still reads as the constant from the leaf — so both the folded
(lit.string) and standalone (constant) roles grade correctly.

Token scopes may now be space-separated; the generic token emit namespaces each
part with langName independently (a no-op for the single-scope case, so the other
grammars stay byte-identical).

YAML scope-gap 99.66% -> 99.75% (lit.string 564->565, exact 99.5%), gap to
official 0.3 pts.

Refs #12

Author: johnsoncodehk

src/gen-tm.ts

@@ -4570,7 +4570,10 @@ export function generateTmLanguage(grammar: CstGrammar, langName: string): TmGra
       // (`variable`) → correctness is unchanged; only the path is finer.
       const emittedScope = tok === identToken ? `${scope}.readwrite` : scope;
       repository[key] = {
-        name: `${emittedScope}.${langName}`,
+        // A space-separated scope (e.g. `string.unquoted constant.language` for a YAML plain
+        // scalar that resolves to a constant) becomes a multi-scope TM name — each part namespaced
+        // with `langName` independently. No-op for the common single-scope case.
+        name: emittedScope.split(' ').map(s => `${s}.${langName}`).join(' '),
         // The bare-identifier rule must scope non-ASCII names too (`Ω`, Cyrillic `А`).
         match: tok === identToken ? identPattern : tokenPatternSource(tok),
       };