Fontify javap buffers in lsp-metals--decode

[LaurenceWarne]

Hi, this PR activates java-mode in javap buffers generated by lsp-metals--decode:

and makes lsp-metals-decode-file a command which when not passed a format-id, will prompt the user for one from a preset list. I've also defconsted all of the format ids so that they're not duplicated.

I hope this is helpful, thanks :slightly_smiling_face:

[kurnevsky]

Thanks.