Validate remaining FP16 instruction features (#8979)

Fixes #8313
## Summary
- Move seven unguarded FP16 unary conversion case labels into the
existing FP16-guarded fallthrough group in `visitUnary`
- Require FP16 for `f32.load_f16` and `f32.store_f16` in
`visitLoad`/`visitStore`
- Add lit regression tests: 7 independent unary modules + 2 independent
memory modules via `foreach`
The SIMDTernary madd/nmadd case from the original report was fixed by
#8403; this PR closes the remaining identifiable FP16 validation gaps
found by audit.

## Test plan
- [x] `build-clang/bin/binaryen-lit test/lit/validation/fp16-unary.wast
-v`
- [x] `build-clang/bin/binaryen-lit test/lit/validation/fp16-memory.wast
-v`
- [x] `build-clang/bin/binaryen-lit test/lit/validation -v`
- [x] `./check.py --binaryen-bin build-clang/bin validator`

Signed-off-by: Gaurav Chaudhary <chaudharygaurav2004@gmail.com>