Add google-java-format formatter for Java

[dbarnett]

Codefmt should implement a google/google-java-format formatter to be used on projects that follow Google's Java style guide such as google/truth.

[dbarnett]

There's a question of default formatter precedence here. It would be nice to avoid using clang-format to format Java code in projects like google-truth even if the user has it configured as the default everywhere else. But how can codefmt know which projects have special formatting rules w/o a long list of manual mappings?

[fowles]

codefmt allows you to set things based on path yes?

[dbarnett]

Yes. The big question here is what should happen if you do:

autocmd FileType java AutoFormatBuffer

and then edit and save files in a project that uses Google style. If we give precedence to the clang-format formatter (which is reasonable given that google-java-format is a special case for Google projects), then clang-format will be applied. Users could tweak the settings for their known Google projects, but that's hit-or-miss, especially for Googlers who will probably want google-java-format to take precedence by default.

[artasparks]

re: @dbarnett

I think it's sufficient to just recommend being explicity about autocmds:

autocmd FileType java AutoFormatBuffer google-java-format