Element custom attribute's styles are only applied on initalization but not on further changes. #7914

Environment
Provide version numbers for the following components (information can be retrieved by running tns info in your project folder or by inspecting the package.json of the project):

• CLI: 6.1.2
• Cross-platform modules:
• Android Runtime: Android 9
• iOS Runtime:
• Plugin(s):

Describe the bug
Element custom attribute's styles are only applied on initalization but not on further changes.

To Reproduce

1. check bgRed value in console by clicking get bgRed // you will get false
2. click toggle to invert bgRed from false to true
3. check bgRed value in console again by clicking get bgRed // you will get true

Expected behavior
background color will change from blue to red after step 2

Sample project
https://play.nativescript.org/?template=play-vue&id=qXgtKz&v=2

Additional context
I can confirm this is not a bug of vue/angular framework as other developer from angular has also reported that this is not work in augular either. Link is provided as follow:

nativescript-vue/nativescript-vue#557 (comment)