LibCpp: Support for parsing c-style fixed arrays (arr[2])

Also adds tests for finding declaration of arrays inside
CppComprehension which requires proper parsing for passing.

Side-effect of this patch: if we ctrl+click on array variables, it
should jump to the correct declaration inside HackStudio.

Userland/Libraries/LibCodeComprehension/Cpp/Tests/find_array_variable_declaration.cpp

@@ -0,0 +1,11 @@
+void foo()
+{
+    int arr[2] = {1,2};
+    arr[1] = 0;
+
+    int arr2[] = {5,6};
+    arr2[0] = 11;
+    
+    int arr3[1][2] = {{3,4}};
+    arr3[0][0] = 72;
+}