fix: layout height issue with Angular forms

[hendrickson-tyler]

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• [x] 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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What is the current behavior?

Margin on field elements change between between invalid and invalid states when using form validation with Angular, which creates an inconsistent experience.

What is the new behavior?

Margin is no longer changed by default.

Fixes #264

[NathanWalker]

Released with https://github.com/NativeScript/theme/tree/v3.1.1