[mlir][LLVM] Let decomposeValue/composeVale pad out larger types (#183825)
Currently, as pointed out in the reviews for #183405, decomposeValues
and composeValues should be able to emit zexts and truncations for cases
like i48 and vector<3xi16> becoming i32s but currently that's an assert.
This commit fixes that limitation.
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>