GDScript: Avoid hard errors on inferred types

Since inference isn't always correct, they are now treated as unsafe
instead of errors.

This also removes inferred type when a variable is reassigned. Since
it's not aware of branching, the types might become invalid in a later
context.

modules/gdscript/tests/scripts/analyzer/features/class_inference_is_weak.gd

@@ -0,0 +1,11 @@
+# https://github.com/godotengine/godot/issues/43503
+
+var test_var = null
+
+
+func test():
+	print(test_var.x)
+
+
+func _init():
+	test_var = Vector3()

modules/gdscript/tests/scripts/analyzer/features/class_inference_is_weak.out

@@ -0,0 +1,2 @@
+GDTEST_OK
+0

modules/gdscript/tests/scripts/analyzer/features/local_inference_is_weak.gd

@@ -0,0 +1,14 @@
+# https://github.com/godotengine/godot/issues/41064
+var x = true
+
+func test():
+	var int_var: int = 0
+	var dyn_var = 2
+
+	if x:
+		dyn_var = 5
+	else:
+		dyn_var = Node.new()
+
+	int_var = dyn_var
+	print(int_var)

modules/gdscript/tests/scripts/analyzer/features/local_inference_is_weak.out

@@ -0,0 +1,2 @@
+GDTEST_OK
+5