Feature Request Expect to open more properties and methods, we have a strong demand for customizing VisualElement

There are many views in our project that need to be customized, especially text input or display-related, so I very much hope that it can be so free in version 2021.2.

For example, these attributes.

Code (CSharp):

1. In the 150th line of TextField.cs, set the access property of the TextInput class to protected to facilitate inheritance and extension.
2. In line 237 of TextInputFieldBase.cs, set the access property of editorEngine in the TextInputBaseField class to protected internal to facilitate inheritance and extension.
3. In line 552 of TextInputFieldBase.cs, set the access property of editorEngine in the TextInputBase class to protected internal to facilitate inheritance and extension.
4. In the 3 lines of TextEditorEngine.cs, set the access property of TextEditorEngine to public to facilitate inheritance and extension.
5. In lines 5 and 6 of TextEditorEngine.cs, set the access properties of OnDetectFocusChangeFunction and OnIndexChangeFunction to public to facilitate inheritance and extension.
6. In the 7th line of TextElement.cs, set the access property of ITextElement to public.
7. In the 5th line of TextInputFieldBase.cs, set the access property in ITextInputField to public.
8. In the 3 lines of TextEditor, set the access property of TextEditorEventHandler to public.
9. In the third line of TouchScreenTextEditor.cs, set the access property of TouchScreenTextEditorEventHandler to public.
10. In Line 9 of TouchScreenTextEditor.cs, set the access property of s_KeyboardOnScreen to public.
11. In line 42 of TextField.cs, set multiline to virtual to facilitate inheritance and expansion.
12. On line 12 of TextField.cs, set the access property of textInput to protected to facilitate inheritance and extension.
13. In line 1186 of VisualElement.cs, set the access property of IncrementVersion to protected internal.
14. On line 24 of Panel.cs, set the access property of VersionChangeType to public.
15. On line 230 of VisualElement.cs, set the access property of isCompositeRoot to protected internal.

Version 2021.2.0a17