[clang][modules] Reset codegen options (take 2). (#74388)

CodeGen options do not affect the AST, so they usually can be ignored.
The only exception to the rule is when a PCM is created with
`-gmodules`.
In that case the Clang module format is switched to object file
container and contains also serialized debug information that can be
affected by debug options. There the following approach was choosen:

1.) Split out all the debug options into a separate `DebugOptions.def`
    file. The file is included by `CodeGenOptions.def`, so the change is
    transparent to all existing users of `CodeGenOptions.def`.
2.) Reset all CodeGen options, but excluding affecting debug options.
3.) Conditionally reset debug options that can affect the PCM.

This fixes rdar://113135909.