JIT: Hoist common mem access out of Then/Else case

Simple example: https://godbolt.org/z/v9788PWh9
`mem` is accessed first in both branches. We should hoist it and consequently do if-conversion.
```cs
static int Hoist(bool cond, ref int mem)
{
int op2;
if (cond)
{
op2 = mem + 1;
}
else
{
op2 = mem + 2;
}
return op2;
}
```
```assembly
Program:Hoist(bool,byref):int (FullOpts):
push rbp
mov rbp, rsp
test dil, dil
jne SHORT G_M31389_IG04
mov eax, dword ptr [rsi]
add eax, 2
jmp SHORT G_M31389_IG05
G_M31389_IG04: ;; offset=0x0010
mov eax, dword ptr [rsi]
inc eax
G_M31389_IG05: ;; offset=0x0014
pop rbp
ret
```

Start with the C# example and its Compiler Explorer output at the linked Godbolt URL, then trace the JIT optimization area responsible for conditional memory accesses. Done means the shared mem load is hoisted before the branches and the generated assembly shows if-conversion without changing the example's result.

Written by the indexing model from the issue text.