[RISC-V] Remove unnecessary assertion from emitOutputInstr (#98484)

* Remove unnecessary assertion

It fired a false positive when W^X was enabled

* Use uint32 write instead of memcpy to be faster

There shouldn't be a problem when we introduce compressed instructions, VF2 supports unaligned stores (sw)
Also, replace compile-time conditions with static_asserts.

* Bring back memcpy because plain RV64 ISA allows trapping on misaligned load/stores

src/coreclr/jit/emitriscv64.cpp

@@ -2118,8 +2118,8 @@ void emitter::emitJumpDistBind()
 unsigned emitter::emitOutput_Instr(BYTE* dst, code_t code) const
 {
     assert(dst != nullptr);
-    assert(sizeof(code_t) == 4);
-    memcpy(dst + writeableOffset, &code, sizeof(code_t));
+    static_assert(sizeof(code_t) == 4, "code_t must be 4 bytes");
+    memcpy(dst + writeableOffset, &code, sizeof(code));
     return sizeof(code_t);
 }
 
@@ -3157,8 +3157,7 @@ size_t emitter::emitOutputInstr(insGroup* ig, instrDesc* id, BYTE** dp)
     instruction       ins;
     size_t            sz = 0;
 
-    assert(REG_NA == static_cast<int>(REG_NA));
-    assert(writeableOffset == 0);
+    static_assert(REG_NA == static_cast<int>(REG_NA), "REG_NA must fit in an int");
 
     insOpts insOp = id->idInsOpt();