Avoid infinite loop checking yield expression

[ghost]

Fixes #21542

The problem was that in checkYieldExpression, we call checkExpressionCached to get the type of the yielded expression. checkExpressionCached resets flowLoopStart, so we don't detect that we're inside a loop in the flow graph.

The fix is that we don't actually need to check the yield expression to get its type -- the type of a yield expression is always anyType, so we can just return that early from getTypeOfExpression.

[sandersn]

You can also fix this by switching back to checkExpression, right? I don't know whether it's good to put more code in getTypeOfExpression, since it's supposed to be a fast path. Opinions @ahejlsberg ?

[sandersn]

Especially if we believe yield to be used rarely, then making yield checking slower is probably the right tradeoff.

[typescript-bot]

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[sandersn]

Turns out the infinite loop has been fixed already. I reverted the code change but kept the test.