Full name of submitter (unless configured in github; will be published with the issue): Hubert Tong

Reference (section label): [lex.token], [lex.pptoken], [lex.phases], [cpp.import], [module.import]

Link to reflector thread (if any): N/A

Issue description:

Consider:

import "myheader.h";

https://wg21.link/module.import describes the phase 7 treatment following the transformation specified by https://wg21.link/cpp.import#4. The grammar for module-import-declaration contains a use of the header-name non-terminal, but header-name‌s are not token‌s (https://wg21.link/lex.token). This means that the conversion from a preprocessing token to a token (https://wg21.link/lex.phases) runs afoul of https://wg21.link/lex.pptoken#2.

Suggested resolution:

Add header-name as an alternative for the token non-terminal, and update [lex.pptoken] paragraph 2 to allow header names.