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/LibCpp/Tests/parser/array-initialization.cpp

@@ -0,0 +1,3 @@
+void foo() {
+    int x[0] = {1,2};
+}