Do not perform full expansion of `#expect()` when `try` or `await` is present.

[grynspan]

For reasons that have been documented at length (see #162), we aren't able to correctly expand conditions on #expect() or #require() that have effects (try or await.) We aren't currently detecting all possible patterns that expand incorrectly. This PR causes us to back out of the full expansion if the try or await keyword is present anywhere inside an expectation condition expression.

Resolves #783.

Checklist:

• [x] Code and documentation should follow the style of the Style Guide.
• [x] If public symbols are renamed or modified, DocC references should be updated.

[grynspan]

@swift-ci test

[grynspan]

@swift-ci test

[grynspan]

@swift-ci test Windows