Improve and package API documentation

• Fix installation of documentation

  The documentation installation directory and the documentation binary package didn't have the API version in; now they do.

• Normalize order of debian/control (wrap-and-sort -abst)

  If we keep the binary packages in a canonical order, it'll minimize spurious diffs later. This is the same principle as sorting lists of files in the build system alphabetically.

• Wrap test dependencies one per line (wrap-and-sort -abst)

  If we keep these in a canonical order and formatting, it'll minimize spurious diffs later. This is the same principle as sorting lists of files in the build system alphabetically.

• architecture: Fill in some brief API documentation

  As much as anything else, this is to check that the documentation build works at all.

• Disable GObject-Introspection by default

  This will make it easier to do CI against SteamRT 1 'scout', which has a very old g-ir-scanner that doesn't work in combination with Meson (for example see https://github.com/ximion/appstream/issues/146). Generating the GObject-Introspection in local test-builds is a useful way to check that the API is "the right shape" for GObject conventions or do rapid prototyping, but we don't expect to use it in production, and we disable it in the packaging.