[Type Checker] Prevent Path Consistency algorithm from aborting too a…

[xedin]

What's in this pull request?

[Type Checker] Prevent Path Consistency algorithm from aborting too aggressively

Instead of failing shrinking when there are no solutions for current
sub-expression, let's restore overload domains for previously solved
sub-expressions and move on trying to solve next expression in the queue.

Resolved bug number: (SR-1794)

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…ggressively

Instead of failing shrinking when there are no solutions for current
sub-expression, let's restore overload domains for previously solved
sub-expressions and move on trying to solve next expression in the queue.

[xedin]

/cc @DougGregor @rudkx

[rudkx]

@swift-ci Test and merge.