[LoongArch] Set some operations action for LSX and LASX

First, expand all truncationg stores and extending loads. Second,
expand everything for `fixedlen_vector_valuetypes`.  Finally, we
selectively turn on ones that can be effectively codegen'd.

Simultaneously, this patch adds floating-point vector types to
load/store patterns. Additional test cases will be included in the IR
instruction test patchs.