unittests/ASM: Adds test for TestNZ bug

Would trigger the bug before it was fixed.

unittests/ASM/FEX_bugs/ShiftConstantBug.asm

@@ -0,0 +1,15 @@
+%ifdef CONFIG
+{
+  "RegData": {
+    "RAX": "0x500000020"
+  }
+}
+%endif
+
+; FEX had a bug in its `TestNZ` opcode where it would try to load a constant in to the tst instruction
+; If the constant didn't fit in a logical encoding it would generate invalid instructions and also crash.
+; This snippet of code was found in libGLX.so.0.0.0 when trying to load steamwebhelper.
+mov     eax, 0x28000001
+shl     rax, 0x5
+
+hlt