[DiagnosticsQoI] SR-3599: Better recovery for decls with consecutive identifiers

[matthewcarroll]

Add diagnostics to fix decls with consecutive identifiers. This applies to
types, properties, variables, and enum cases. The diagnostic adds a camel-cased option if it is different than the first option.

let a b = 0
// error: found an unexpected second identifier in variable declaration; is there an accidental break?
// note: join the identifiers together
  var a b = 0
      ~~^
      ab

https://bugs.swift.org/browse/SR-3599

[slavapestov]

@swift-ci Please smoke test

[slavapestov]

Looks like you accidentally fixed a compiler_crasher.

[matthewcarroll]

@slavapestov,

Would you like me to remove the expectation of crashing in the test 28619-basety-islvaluetype-basety-is-anymetatypetype?

[CodaFi]

@matthewcarroll If you want to automate the process,

../llvm/utils/lit/lit.py -sv ../build/Ninja-DebugAssert/swift-macosx-x86_64/validation-test-macosx-x86_64/compiler_crashers/ | ./utils/resolve-crashes.py

[matthewcarroll]

@slavapestov, @CodaFi,

Thanks! I ran the script on the test.

[DougGregor]

@swift-ci please smoke test

[DougGregor]

@swift-ci please smoke test