Allow the user to emit extra fake modules

[Gankra]

A common annoyance for browsers is that we have a bunch of pages allocated by the JIT in a range of memory that is effectively a secret self-modifying module. One of the simplest and cleanest ways to make everything down the line understand this would be to allow the crashing process to tell minidump-writer about such "secret modules"

For spidermonkey's purpose, literally all that matters is the location+size, and a name. Things like codefiles/debugfiles could be junk/magic, but I would need to test that.

[moztcampbell]

In the breakpad clients, I see an AddMappingInfo that looks like the same concept.

https://searchfox.org/mozilla-central/rev/6ec440e105c2b75d5cae9d34f957a2f85a106d54/toolkit/crashreporter/breakpad-client/linux/handler/exception_handler.h#218-222