The --pre-glob flag is like the --glob flag, except it applies to filtering
files through the preprocessor instead of for search. This makes it
possible to apply the preprocessor to only a small subset of files, which
can greatly reduce the process overhead of using a preprocessor when
searching large directories.
This basically rewrites every integration test. We reduce the amount of
magic involved here in terms of which arguments are being passed to
ripgrep processes. To make up for the boiler plate saved by the magic,
we make the Dir (formerly WorkDir) type a bit nicer to use, along with a
new TestCommand that wraps a std::process::Command. In exchange, we get
tests that are easier to read and write.
We also run every test with the `--pcre2` flag to make sure that works,
when PCRE2 is available.
