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.
original_source_maps_complete indicates whether the original_source_maps cover the whole
map, i.e. whether every module that ended up in mappings had an original sourcemap.