meson: parse TAP output generated by our tests

meson: parse TAP output generated by our tests

By default, Meson only knows to pay respect to the exit code of tests to
judge whether or not it ran successfully. This can be changed though by
specifying the "protocol" parameter. Next to the default "exitcode"
protocol, Meson also supports the "tap" output that our tests already
know to generate.

Unfortunately, the "tap" protocol was incompatible with `meson test
--interactive` and caused a hang. We have upstreamed a fix [1] though,
so with the recent release of Meson 1.8 that fix is finally out and we
can start using the "tap" protocol when running with a recent-enough
version of this build tool.

With this change in place, Meson now properly detects how many subtests
ran and whether test suites have been skipped:

    ```
    $ meson test t002*
    ninja: Entering directory `/home/pks/Development/git/build'
     1/10 t0024-crlf-archive                  OK              0.17s   2 subtests passed
     2/10 t0022-crlf-rename                   OK              0.18s   2 subtests passed
     3/10 t0029-core-unsetenvvars             SKIP            0.15s
     4/10 t0023-crlf-am                       OK              0.18s   2 subtests passed
     5/10 t0025-crlf-renormalize              OK              0.21s   3 subtests passed
     6/10 t0026-eol-config                    OK              0.25s   5 subtests passed
     7/10 t0020-crlf                          OK              0.81s   36 subtests passed
     8/10 t0028-working-tree-encoding         OK              0.85s   22 subtests passed
     9/10 t0021-conversion                    OK              3.45s   38 subtests passed
    10/10 t0027-auto-crlf                     OK             26.35s   2600 subtests passed

    Ok:                9
    Fail:              0
    Skipped:           1
    ```

Note that when running `meson test --interactive` the test results will
now be marked as "ignored". This is because in interactive mode the file
descriptors will remain connected to the user's terminal, and it is
expected that the user interacts with the tests (e.g., spawn a debugger
or use `test_pause`). As such, the TAP output cannot be parsed reliably
by Meson in that case, so the tests are marked as ignored accordingly.

[1]: https://github.com/mesonbuild/meson/pull/13980

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>