Add feature to produce serialized diagnostics files

[brentleyjones]

Using the serialized_diagnostics_file feature will add the --serialized-diagnostics flag to C/C++/Objective-C/Objective-C++ compiles, causing a declared.dia file output to be produced.

Closes #15191.

[brentleyjones]

cc @oquenchil @meteorcloudy @DavidGoldman

[meteorcloudy]

@googlewalt Do you think you are the right person to review this?

@oquenchil Since this feature seems not only apply to objc rules, maybe you should also take a look?

[oquenchil]

Hi Brentley, through no fault of your own this involves a lot of piping in the codebase just to tell Bazel about a new file being produced during compilation. Can you think of a way this could work using additional outputs?. I would already consider it a win if we don't have to know about that additional extension.

Thanks.

[brentleyjones]

Sure, I'll take a look today to see if I can use that.

[brentleyjones]

From the looks of it, that will shift a small amount of code from CppCompileActionBuilder.setOutputs() to CppCompileActionBuilder.setAdditionalOutputs().

Because of it being a feature_flag, we still need to know about the extension and whatnot for addStringVariable(). I'm not really sure there is much of a win in refactoring this, and honestly there is a higher chance of me messing things up when I'm pretty sure the change as is works. I think it can get better if we eventually move to the inject like design (#15191 (comment)) but that is out of scope for this change, as I would like to get this into the 5.2 release as well.

[brentleyjones]

Friendly ping @oquenchil.

[oquenchil]

LGTM

[brentleyjones]

Thanks @oquenchil. Can I get this imported?