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 new behavior?

This PR gets rid of type errors related to some computed setNative methods.
Since we use symbols to define methods with a single argument, TypeScript may complain about union string types for prototype's [prop: symbol].
Things can get a bad turn if some methods use any as an argument type or unions/enums end up in conflict with string type.

To solve this, the following actions have been performed:

• Replaced argument any with the corresponding type
• Replaced string enum with string type
• Switched order of some computed method declarations to get rid of union type conflicts

A small example to understand the conflict:

	[testIDProperty.setNative](value: string) {
		this.setAccessibilityIdentifier(this.nativeViewProtected, value);
	}

        // This throws error as TS with cause enum to have conflict with expected string type
        [accessibilityStateProperty.setNative](value: AccessibilityState): void {
		this.accessibilityState = value as AccessibilityState;
		updateAccessibilityProperties(this);
	}

And this will work because TS doesn't know about expected string argument yet.

	[accessibilityStateProperty.setNative](value: AccessibilityState): void {
		this.accessibilityState = value as AccessibilityState;
		updateAccessibilityProperties(this);
	}
	
	[testIDProperty.setNative](value: string) {
		this.setAccessibilityIdentifier(this.nativeViewProtected, value);
	}