[InstCombine] Teach SimplifyMultipleUseDemandedBits to handle And/Or/Xor known...

[InstCombine] Teach SimplifyMultipleUseDemandedBits to handle And/Or/Xor known bits using the LHS/RHS known bits it already acquired without recursing back into computeKnownBits.

This replicates the known bits and constant creation code from the single use case for these instructions and adds it here. The computeKnownBits and constant creation code for other instructions is now in the default case of the opcode switch.

llvm-svn: 300094