Expose line-mapping for decompiled jars

[zml2008]

This also fixes a case where the tracer wasn't incremented,
which caused misaligned linemaps.

I've tested this in my work on VanillaGradle, seems to make the debugger way happier now.

See VanillaGradle's implementation for an example of linemapping being applied.

There should be no impact on the decompiled output -- this whole bytecode tracer infrastructure is only used for the -bsm flag.

[LexManos]

What is the use case? What does this actually do that is useful?

[zml2008]

In an environment where you're not recompiling, this tells Fernflower to spit out a mapping of the lines in bytecode to lines in decompiled code. That is needed for breakpoints set based on the source in-IDE to match up with the code executed.

Without linemapping, method breakpoints will open up at (from our view) random points in the class file, and line breakpoints often won't trigger at all.

[LexManos]

Interesting idea, this might be useful to provide MCPConfig builds, that do not have patches to make the code recompile.
Thanks for adding yet another thing onto my todo list ;)