Forward blockparams to critical edge blocks

Our block lowering order currently inserts new blocks on critical edges to enable register allocation. When these blocks are inserted on edges that targeted blocks with block params, we add block params to the new block, and forward all of its block parameters to the original target through an unconditional branch.

We could simplify this by instead removing the block parameters from the original branch instruction, and adding them only to the block inserted to split the critical edge. We would need to modify the following case in the machinst lowering code, to instead of processing the block params for each branch of a conditional branch, move the processing of those blockparams to the critical edge splitting block.

https://github.com/bytecodealliance/wasmtime/blob/5c8bce70a11657ad6740f56a852f64d147f93494/cranelift/codegen/src/machinst/lower.rs#L1060-L1073

This should be a fine transformation to make, as the critical edge splitting block will be dominated by the block that defines the values that will be passed through to the blockparams of the original successor.