FEX: Rebrand FEXInterpreter as FEX

Still creates a copy of FEXInterpreter from FEX for downstream projects
to have some time to get off the old name. Creating a symlink is kind of
a pain in cmake so just doing an install copy is easy.

Scripts/guest_test_runner.py

@@ -6,7 +6,7 @@ import subprocess
 
 # Check if FEX indicates support for AVX
 def DoesFEXSupportAVX(mode):
-    fex_interpreter_path = os.path.dirname(sys.argv[7]) + "/FEXInterpreter"
+    fex_interpreter_path = os.path.dirname(sys.argv[7]) + "/FEX"
 
     args = list()
     args.append(fex_interpreter_path)