wasm: use primitive opcodes for fabs and sqrt
- Add new `WasmInstr` constructor `WasmSqrt` for sqrt, corresponding to primitivie operations in wasm. - When lowering CallishMachOp, use `WasmAbs` and `WasmSqrt` for F32 and F64 fabs and sqrt. (cherry picked from commit 64b0d4d0)
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