Add cabal-testsuite helpers

[9999years]

Needed for #10292.

The assertGlob family of helpers allow tests to assert that a glob matches at least one path (or alternatively, matches no paths). These are useful for matching temporary files, which can have arbitrary suffixes. The Glob package is used instead of Cabal's built-in glob-matching facility because Cabal's glob-matching logic doesn't allow wildcards in the middle of a filename, e.g. tmp-* or haddock-response*.txt.

The assert{Any,No}FileContains helpers allow tests to assert that at least one path in a list contains a given string (or alternatively, that no paths in a list contain a given string). These work nicely with lists of globs.

• Patches conform to the coding conventions.
• Is this a PR that fixes CI? If so, it will need to be backported to older cabal release branches (ask maintainers for directions).

[9999years]

Rebased manually to fix mergify (!)