Add man pages for gi-* tools

Resolves: #3260 (closed)

Now based on !3928 (merged) because otherwise it would be factually incorrect.

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• Merge g-ir-compiler, g-ir-generate man pages from gobject-introspection (via git filter-repo, slightly rewriting one commit message to fix a GitLab issue reference)

• Remove generated .1 files, keeping only .rst source

• Rename man pages to the tools' GLib names

• Add metadata header to gi-* man pages

• Spell Matthias' name correctly in the gi-* man pages

  This was wrong since 2008.

• Retitle gi-* man pages and update content

• g-ir- tools: Add examples to man pages

• Add gi-* man pages to the build system

• Add a man page for gi-inspect-typelib

/cc @pwithnall @ebassi