meson: Add tags/cscope custom targets for meson

This adds a script that generates the files to be fed to ctags/cscope
programs and adds a few custom targets for meson to generate the databases like
we had in autotools.

Signed-off-by: Marius Vlad <marius.vlad@collabora.com>
2 jobs for meson-tags-cscope in 6 minutes and 36 seconds (queued for 38 seconds)
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passed #197793
build-native-autotools

00:06:36

passed #197794
build-native-meson

00:03:41