Add test case for async try foo()

Ensure that we emit the proper diagnostics for when the await and try
are flipped, but also await is incorrectly spelled `async`.

We're expecting two diagnostics, both of which have fix-its that do the
right thing. One will just replace the `async` with an `await`. The
other will move the text so that try comes first. Because `await` and
`async` are both have the same number of characters, both fix-its will
fix the issue correctly.

Author: etcwilde

test/Concurrency/await_typo_correction.swift

@@ -14,6 +14,10 @@ func async() throws { }
     // expected-error@+1 {{found 'async' in expression; did you mean 'await'?}}{{9-14=await}}
     try async asyncFunc()
 
+    // expected-error@+2 {{found 'async' in expression; did you mean 'await'?}}{{5-10=await}}
+    // expected-warning@+1 {{'try' must precede 'await'}}{{5-11=}}{{15-15=await }}
+    async try asyncFunc()
+
     // expected-error@+1 {{found 'async' in expression; did you mean 'await'?}}{{13-18=await}}
     let _ = async anotherAsyncFunc()