Add more tags to the list of things the decompiler can handle. This
required some changes to track the containing object class in the
DecompileCtx, since some objects use the same tag names.
The improved support means we can test the decompiler on most of the
test suite. Any new test samples will by default be tested to ensure the
decompiler produces the original blueprint file.
Also, updated the decompiler to always use double quotes.
`blueprint-compiler port` interactively ports a project to blueprint.
It will create the subproject wrap file, add it to .gitignore, decompile
your GtkBuilder XML files, emit code to copy and paste into your
meson.build file, and update POTFILES.in.
It can't quite handle all of the features the forward compiler can, so
it will skip those files.
