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?

There are cases when core splices arrays using a negative index.
This can have bad consequences as splice negative index counts back from the end of the array.
For example, calling LayoutBase.removeChild to remove a view that is not an actual child will unexpectedly remove an existing child from the caller layout.

What is the new behavior?

Added index checking for 4 array splice calls that were error-prone.