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.
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• 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?

There are cases when TextBase and Span background colors mismatch.
That is very apparent when tapping a button with spans and css :pressed pseudo-state.

What is the new behavior?

Spans will be colorless (transparent) to display TextBase parent background color unless they or their FormattedString parents have a background color of their own.
This issue was partially fixed on android but also broke FormattedString color inheritance, so this PR fixes that too (see #10682).

Fixes/Closes #7379 .