vkd3d-shader/preproc: Parse comments in #include and #line directives.
vkd3d-shader/preproc: Swap to the INITIAL state after ending a buffer.
vkd3d-shader/preproc: Store EOF state per buffer. We may immediately push a new file or expansion. Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=43481