GDScript: Begin making constants deep, not shallow or flat

modules/gdscript/tests/scripts/analyzer/errors/constant_array_index_assign.gd

@@ -0,0 +1,5 @@
+const array: Array = [0]
+
+func test():
+	var key: int = 0
+	array[key] = 0

modules/gdscript/tests/scripts/analyzer/errors/constant_array_index_assign.out

@@ -0,0 +1,2 @@
+GDTEST_ANALYZER_ERROR
+Cannot assign a new value to a constant.

modules/gdscript/tests/scripts/analyzer/errors/constant_dictionary_index_assign.gd

@@ -0,0 +1,5 @@
+const dictionary := {}
+
+func test():
+	var key: int = 0
+	dictionary[key] = 0

modules/gdscript/tests/scripts/analyzer/errors/constant_dictionary_index_assign.out

@@ -0,0 +1,2 @@
+GDTEST_ANALYZER_ERROR
+Cannot assign a new value to a constant.