Use Cmt to evaluate Cond and Elem during match to avoid building the
nested capture structure later.

This change fixes an issue where glob patterns like `{a,ab}` would not
match `ab` because the first option `a` matches, then the end of the
string is expected but `b` is found, and LPeg does not backtrack to try
the next option `ab` which would match. The fix here is to also append
the rest of the pattern to the generated LPeg pattern for each option.
This changes a glob `{a,ab}` from being parsed as

    ("a" or "ab") "end of string"

to

    ("a" "end of string" or "ab" "end of string")

Here, matching against `ab` would try the first option, fail to match,
then proceed to the next option, and match.

The sacrifice this change makes is dropping support for nested `{}`
conditions, which VSCode doesn't seem to support or test AFAICT.

Fixes #28931

Co-authored-by: Sergey Slipchenko <faergeek@gmail.com>

refactor(lsp): move glob parsing to vim.glob

Moving the logic for using vim.lpeg to create a match pattern from a
glob into `vim.glob`. There are several places in the LSP spec that
use globs, and it's very useful to have glob matching as a
generally-available utility.