remove the stateful jl_parse_next API

[JeffBezanson]

With this change, we parse a whole file at once to a toplevel expression with interleaved line nodes. This is much simpler.

cc @yuyichao

[yuyichao]

👍

[JeffBezanson]

Looks like #14705

[tkelman]

just double checking, the mechanism for __precompile__ doesn't depend on this incremental parsing, does it?

[JeffBezanson]

I don't believe so; this should only affect the stage before macro expansion, so no julia code is running.

[maleadt]

Can the jl_parse_next forward declaration in src/julia_internal.h be removed too? There also seem to be some references to the API in devdocs/init.rst and src/ast.c.

[JeffBezanson]

Ah yes, thanks for finding those.