Unify error and warning locations reporting in the console

At the moment, Compiler.java rewrites the location of an error (elision of the absolute file path), while leaving the location of a compiler warning in its raw form.

Would be nice to have all the paths elided, no?

Doing this would also simplify the task of jumping to warning locations from the console, as has been requested in #3383

Start by reading Compiler.java and compare how compiler errors and warnings are formatted before reaching the console. Make the warning location handling consistent with error reporting so absolute paths are elided, then verify that both message types show the shortened locations and remain usable for console navigation.

Written by the indexing model from the issue text.