Function tokenizeWithTriplate

Tokenizes a document that may use Triplate templating, opt-in. Default host lexing is unaffected: a non-template document is tokenized exactly as lexer.tokenize(text) would, and Triplate token types never appear in any host token list.

For a template, the host parser should consume TriplateLexingResult.parseTokens (placeholders) while every other consumer uses TriplateLexingResult.tokens (the faithful stream). The frontmatter's prefixed-name/IRI/literal values are surfaced as real RDF tokens (via triplate's positioned symbols) so tooltips and prefix rename work inside it; if triplate reports nothing usable it falls back to a single opaque TRIPLATE_FRONTMATTER block.