Improve error message for parsing errors

Summary

When encountering an invalid character during parsing, spack should give the user some indication of where the error lies.

Rationale

Being new to writing spack recipes, my new recipe included the line

    depends_on('cuda >=10.2', when='+cuda')

which is not the correct way of expressing version range.

The corresponding error message was

$ spack install mypackage %intel +openmp 
==> Error: Invalid character

which did not tell me which file was affected, nor which line / string was the problem and made it very difficult to track down.

Adding -v or --show-log-on-error did not lead to a more verbose error message.

Description

For example, instead of
https://github.com/spack/spack/blob/8d118104c79bca646b193f84857b75b7f54359df/lib/spack/spack/parse.py#L80

do something like

raise LexError(f"Invalid character in word '{word}'", word, word.index(remainder))

(or make sure to include the metadata of the LexError when displaying the exception).

Additional information

spack --version
0.17.1-1249-8a8b01328b

General information

• I have run spack --version and reported the version of Spack
• I have searched the issues of this repo and believe this is not a duplicate

Start in lib/spack/spack/parse.py at the linked LexError handling and inspect how parsing exceptions are displayed for the shown spack install command. Done means an invalid character error identifies the affected file and the relevant line or string, with useful LexError metadata included in the output.