Optimize conditions with compile time Booleans

[swernli]

This change optimizes handling of conditions where some of the values are known compile time Boolean values. In particular, it expands handling of if-elif-else sequences by compressing known true branches into the current block and skipping any other branches. Likewise, for compound conditional evaluation it adds handling for special cases where part of a logical and or logical or statement is known to be constant, removing the need for a phi-node and propagating the appropriate constant or dynamic value.

New and updated test cases were manually verified for correct output.

[swernli]

/azp run

[azure-pipelines[bot]]

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