[WebAssembly] Update the test for half (NFC)

Replace the existing `f16` test with the version that is uses for other
architectures (typically as `half.ll`). This still covers the
conversions from the existing test, but also adds checks for most simple
ops.

Additionally, rename `half-precision.ll` to `fp-intrinsics.ll` to keep
the name similar to this test.

Author: tgross35

llvm/test/CodeGen/WebAssembly/half-precision.ll renamed to llvm/test/CodeGen/WebAssembly/f16-intrinsics.ll

@@ -1,5 +1,7 @@
 ; RUN: llc < %s --mtriple=wasm32-unknown-unknown -asm-verbose=false -disable-wasm-fallthrough-return-opt -wasm-disable-explicit-locals -wasm-keep-registers -mattr=+fp16,+simd128 | FileCheck %s
 
+; Tests for `llvm.wasm.*.*f16` intrinsics
+
 declare float @llvm.wasm.loadf32.f16(ptr)
 declare void @llvm.wasm.storef16.f32(float, ptr)