feat: add sys:// ios images

[edusperoni]

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• 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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• Tests for the changes are included - https://github.com/NativeScript/NativeScript/blob/master/tools/notes/WritingUnitTests.md.

What is the current behavior?

No easy drop in support for SF Symbols https://developer.apple.com/sf-symbols/

What is the new behavior?

You can now use sys:// prefix with any symbol name on an Image to use. Image also supports symbolEffect property providing an interface to enable effects on symbols.