PR Checklist

• The PR title follows our guidelines: https://github.com/NativeScript/NativeScript/blob/master/tools/notes/CONTRIBUTING.md#commit-messages.
• There is an issue for the bug/feature this PR is for. To avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it.
• 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.
• Tests for the changes are included - https://github.com/NativeScript/NativeScript/blob/master/tools/notes/WritingUnitTests.md.

What is the current behavior?

Right now, views can only have a single box-shadow.

What is the new behavior?

Views can have multiple box-shadows.

Few improvements to note:

• Android shadows will respect transparent background without the need of an overlay layer
• Android shadows will render a solid shadow when blur radius is <= 0
• Added multipliers to match native shadow blur with CSS shadow blur based on discussion in fix(ios): consistent box-shadow radius blur #10583

Fixes/Implements/Closes #[Issue Number].

BREAKING CHANGES:

Shadow blur changes to match the CSS shadow blur.
The formulas are based on these sources:
https://bjango.com/articles/matchingdropshadows

Apple UX guide also confirms the iOS formula:
https://microsoft.github.io/apple-ux-guide/Shadows.html