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?

Switches cannot be styled using the :checked pseudo selector.
Switch color behavior differs between iOS and Android.
Android Switch colors are muted and not same as set.

What is the new behavior?

Switches can now be styled with the :checked selector.
Switches now have the same behavior across iOS and Android.
Switch colors are exactly as set (no color filters etc applied).

.switch-demo-page Switch.custom-switch {
    color: #ddd;
    background-color: #65adf1;
}

.switch-demo-page Switch.custom-switch:checked {
    color: #111;
    background-color: #65adf1;
}

.switch-demo-page Switch.custom-switch:disabled {
    color: #777;
    background-color: #ddd;
}

.switch-demo-page Switch.custom-switch:disabled:checked {
    color: #ddd;
    background-color: #777;
}

BREAKING CHANGES:

Switch color now affects both unchecked and checked states on iOS
Switch backgroundColor now affects both checked and unchecked states on iOS
Switch colors are now exactly as specified without any color filtering on Android (no more muted colors)

Migration: update color, backgroundColor and offBackgroundColor values (inline or in css) to the desired colors.