GDScript: Begin making constants deep, not shallow or flat

modules/gdscript/tests/scripts/runtime/errors/constant_array_is_deep.gd

@@ -0,0 +1,6 @@
+const array: Array = [{}]
+
+func test():
+	var dictionary := array[0]
+	var key: int = 0
+	dictionary[key] = 0

modules/gdscript/tests/scripts/runtime/errors/constant_array_is_deep.out

@@ -0,0 +1,6 @@
+GDTEST_RUNTIME_ERROR
+>> SCRIPT ERROR
+>> on function: test()
+>> runtime/errors/constant_array_is_deep.gd
+>> 6
+>> Invalid set index '0' (on base: 'Dictionary') with value of type 'int'

modules/gdscript/tests/scripts/runtime/errors/constant_array_push_back.gd

@@ -0,0 +1,4 @@
+const array: Array = [0]
+
+func test():
+	array.push_back(0)

modules/gdscript/tests/scripts/runtime/errors/constant_array_push_back.out

@@ -0,0 +1,7 @@
+GDTEST_RUNTIME_ERROR
+>> ERROR
+>> on function: push_back()
+>> core/variant/array.cpp
+>> 253
+>> Condition "_p->read_only" is true.
+>> Array is in read-only state.

modules/gdscript/tests/scripts/runtime/errors/constant_dictionary_erase.gd

@@ -0,0 +1,4 @@
+const dictionary := {}
+
+func test():
+  dictionary.erase(0)

modules/gdscript/tests/scripts/runtime/errors/constant_dictionary_erase.out

@@ -0,0 +1,7 @@
+GDTEST_RUNTIME_ERROR
+>> ERROR
+>> on function: erase()
+>> core/variant/dictionary.cpp
+>> 177
+>> Condition "_p->read_only" is true. Returning: false
+>> Dictionary is in read-only state.

modules/gdscript/tests/scripts/runtime/errors/constant_dictionary_is_deep.gd

@@ -0,0 +1,6 @@
+const dictionary := {0: [0]}
+
+func test():
+	var array := dictionary[0]
+	var key: int = 0
+	array[key] = 0

modules/gdscript/tests/scripts/runtime/errors/constant_dictionary_is_deep.out

@@ -0,0 +1,6 @@
+GDTEST_RUNTIME_ERROR
+>> SCRIPT ERROR
+>> on function: test()
+>> runtime/errors/constant_dictionary_is_deep.gd
+>> 6
+>> Invalid set index '0' (on base: 'Array') with value of type 'int'