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.ast

@@ -0,0 +1,19 @@
+TranslationUnit[0:0->2:0]
+  FunctionDeclaration[0:0->2:0]
+    NamedType[0:0->0:3]
+      void
+    foo
+    (
+    )
+    FunctionDefinition[0:11->2:0]
+    {
+      VariableDeclaration[1:4->1:20]
+        NamedType[1:4->1:6]
+          int
+        x
+        BracedInitList[1:15->1:20]
+          NumericLiteral[1:16->1:16]
+          1
+          NumericLiteral[1:18->1:18]
+          2
+    }