Do not restore the precedencegroup name when deserializing them.

[rudkx]

We only need to have the identifier during type checking of operator
declarations, so we do not need to restore it from the
PrecedenceGroupDecl during deserialization. We can just use the
deserialized name from the PrecedenceGroupDecl directly if needed.

This does result in one change in behavior. When printing modules, we
previously didn't print 'DefaultPrecedence' for items that had no
precedence specified, but now we will as seen in the test update for
IDE/print_ast_tc_decls.swift.

[rudkx]

@benlangmuir I'm not sure how faithful we're attempting to be with the input source in module printing. Does the output different in the test case that I updated matter?

[rudkx]

@swift-ci Please smoke test

[slavapestov]

I think the textual module interface printing stuff will print deserialized decls when you’re producing a textual interface in non-WMO mode because the printing is performed during the merge modules phase. Cc @harlanhaskins

[harlanhaskins]

@slavapestov Yep, and I think this behavior change should be okay for that, provided we aren’t losing information. This does however highlight the lack of tests for operator decls in test/ParseableInterface/. Also, do we currently print the operator protocol work you did recently, @rudkx?

[rudkx]

@harlanhaskins We print that type, but I don't think we have tests for it yet. I'm working on enhancing it to allow for multiple types to be specified, and will make sure I add some printing tests when I do that.