Convert BuildTarget arguments explicitly in the interpreter

[dcbaker]

This allows us to have a fully functional conversion with type checking of the kwargs dictionaries between the DSL level and and the Build level of abstractions. Apart from fixing a number of incorrect or incomplete annotations, this gets us to the point that we can (mostly) validate the type checking.

This is set as draft because I'm sure there are regressions that don't show up on my system but will light CI up like a christmas tree.

[dnicolodi]

The commit message says dict[str, str] but this is dict[str, ElementaryOptionValues]

[bonzini]

The errors seem to be always the same changes in error messages:

expected "test cases/failing/64 skip only subdir/meson.build:8:0: ERROR: File main.cpp does not exist." not found in stdout 
...
mesonbuild.interpreterbase.exceptions.InterpreterException: Tried to add non-existing source file main.cpp.

But there's also one where the old message is better:

expected "test cases/failing/133 java sources in non jar target/meson.build:3:0: ERROR: Build target of type "executable" cannot build java source: "Test.java". Use "jar" instead." not found in stdout 
...
  File "/__w/meson/meson/mesonbuild/build.py", line 1128, in process_compilers
    raise MesonException(m)
mesonbuild.utils.core.MesonException: No host machine compiler for 'Test.java'