[lex.pptoken] "Whitespace" and "whitespace characters" should be definitions

[eisenwave]

The index points to https://eel.is/c++draft/lex.pptoken#1 as the place where "whitespace" is introduced.

The terms "whitespace" and "whitespace character" are quasi-definitions within that paragraph, and they should be formatted as such (i.e. in italics).

There are many places where [lex] refers to whitespace, so by all means, it should be a defined term.

[eisenwave]

This issue is essentially obsoleted if cplusplus/papers#2287 is accepted. Even if not, it's worth keeping in mind that we could do something editorially here.

Also worth keeping in mind that we may want to remove the index entry for "whitespace" once whitespace-character is a formal term.

[AlisdairM]

See also #7359, https://wg21.link/P2348, and cplusplus/papers#1027, although naturally I prefer my own paper :)

[eisenwave]

Alright, we're already tracking this in a bunch of papers. I don't think this issue is helping.

[AlisdairM]

Talking with the author, it is not clear whether P2348 will be revised. Meanwhile, cplusplus/papers#2287 provides a definition for only whitespace character, and not for the broader term of whitespace --- potentially left as follow-up work.

I think this issue may still be useful to track the progress of different wordings until definitions for both terms land in the draft.