[WebAssembly] Autogenerate tests for simd-select.ll

Updating the simd-select.ll tests manually with consistent named
regexps for the register numbers was taking more time than it was
worth, so this patch updates that test file to have autogenerated
output. This is not a significant readability regression because the
tests in that file are all very small.

Depends on D83734.

Differential Revision: https://reviews.llvm.org/D83736