[lldb][test][NFC] Rename Language.cpp to LanguageTest.cpp

So it's consistent with the other tests in this directory.

Also aligns with the source file header comment.

Author: Michael137

lldb/unittests/Target/CMakeLists.txt

@@ -2,7 +2,7 @@ add_lldb_unittest(TargetTests
   ABITest.cpp
   DynamicRegisterInfoTest.cpp
   ExecutionContextTest.cpp
-  Language.cpp
+  LanguageTest.cpp
   LocateModuleCallbackTest.cpp
   MemoryRegionInfoTest.cpp
   MemoryTest.cpp