[W-21481438] feat: add multiline string support for Apex grammar

[peternhale]

Summary

Adds grammar support for Apex multiline strings ('''...''') and template expressions (${var}).

Changes

• Grammar (apex.tmLanguage.yml)

  • New multiline-string-literal pattern (''' begin/end)
  • Updated string-literal so ''' is not parsed as single-quote ('(?!'') lookahead)
  • New string-template-expression for ${...} in single and multiline strings

• Generated grammars

  • apex.tmLanguage, apex.tmLanguage.cson, soql.tmLanguage regenerated with the new rules

• Tests (literals.test.ts)

  • Simple multiline string, template expressions, escaped characters
  • Method args, return values, SOQL WHERE, Map literals, throw, annotations, initializer blocks
  • Token types extended for multiline strings and template expressions

• Repro fixtures

  • MultiLineString.cls and meta.xml for manual checks

@W-21481438@

[peternhale]

@mshanemc why this test? The source is not valid.

[{
"resource": "/Users/peter.hale/git/dreamhouse-lwc-clean/force-app/main/default/classes/ManyInterfaces.cls",
"owner": "generated_diagnostic_collection_name#8",
"severity": 8,
"message": "Missing '' at 'public'",
"startLineNumber": 5,
"startColumn": 1,
"endLineNumber": 5,
"endColumn": 7,
"modelVersionId": 41,
"origin": "extHost1"
}]