fix(core): CSS style not working properly in Android modal pages

[dgmachado]

PR Checklist

• The PR title follows our guidelines: https://github.com/NativeScript/NativeScript/blob/master/tools/notes/CONTRIBUTING.md#commit-messages.
• You have signed the CLA.
• All existing tests are passing: https://github.com/NativeScript/NativeScript/blob/master/tools/notes/DevelopmentWorkflow.md#running-unit-tests-application.

What is the current behavior?

When app is set with force light mode settings, the styling on modal page is not working if having .ns-light identifier.

Please find the sample app and screen recording attached. (run npm i first)

Steps to reproduce:

1) Tap on 'MODAL' actionbar item to show a modal page.
2) Notice the 'Testing: 1' label on the modal page is in grey color even though on app.android.css, the Label type is styled as red color. 

modal_frame_cssclass_issue.mov

What is the new behavior?

Fixes/Implements/Closes #[Issue Number].

The css is being applied properly.

Sample app:
testPopoverModal.zip

[farfromrefug]

@dgmachado awesome fix!!! Might be fixing another issue of mine