Support `parse_file`

[oovm]

Add parse_file function like syn::parse_file.

Helps implement single-file components, or a more native experience of tsx without the html! macro.

[vldm]

Hi, Could you clarify the necessity of this—why can’t the file simply be opened separately and read using the interface from https://docs.rs/rstml/latest/rstml/struct.Parser.html?

In syn, as I understand it, the main motivation is to get rid of the shebang (and also the UTF BOM).

In rstml, there are several modes, and adding any specialized entrypoints would require duplicating them for each mode (proc-macro/proc-macro2, recoverable errors, config). That’s why I’d actually prefer to keep only the most essential methods.

Also rstml is bound to proc-macro/proc-macro2 and I am not sure that it is good to hide those details from users.