Without the `-Xmultifile-parts-inherit` mode for now.
This is implemented as follows: FileClassLowering collects information
about multifile parts and the corresponding facades, which a later
GenerateMultifileFacades phase uses to generate new IrFile instances and
add it to the module fragment that's being compiled.
Note that GenerateMultifileFacades is in the end of lowering phases
because delegates in the facade should be generated for all additional
functions generated by certain lowerings (default arguments,
JvmOverloads, etc.). If GenerateMultifileFacades was right after
FileClassLowering, they would still be generated, but we'd then process
them in lowerings mentioned above, which would result in duplicated
logic in the bytecode. There's a new bytecode text test which checks
that this doesn't happen for functions with default arguments.
All bytecode text tests are run with stdlib in the classpath and only
for JVM backend, therefore directives WITH_RUNTIME, TARGET_BACKEND,
IGNORE_BACKEND are not needed
Preserve static initialization semantics for parts by introducing a special "clinit trigger" class.
Insert "static initialization trigger" call to every method of a part class, remove this call on inline.
Always mangle names for private functions in multifile class parts to avoid resolution clashes on inheritance.
NB in codegen tests initializers for all non-const vals are wrapped in 'run { ... }',
so that the initializer is not a constant expression, and some static initialization code should be generated.
