Collects identifier names and their byte positions from an AST.
This is used to populate the names field in source maps.
Based on swc_compiler_base::IdentCollector.
A config to generate a source map which includes the source content of every
source file. SWC doesn’t inline sources content by default when generating a
sourcemap, so we need to provide a custom config to do it.
Generates a [StructuredSourceMap] for the transformed code, whose sourcesContent
entries are individual shared ropes instead of being embedded in the serialized JSON. This
keeps later sources URL rewrites and map embedding from copying the source text of every
module. Serialize with [StructuredSourceMap::to_rope] where raw bytes are needed.