toAnnotatedString

Resolves this line's spans against theme and returns the styled AnnotatedString.

SyntaxTheme.baseStyle is applied first over the whole text, then each span in HighlightedLine.spans order, so later spans merge over earlier ones (Compose addStyle semantics). Offsets are UTF-16. Spans whose capture does not resolve are skipped. SyntaxTheme.background is never read.