Add support for parsing shorthand property assignments.
Add the IPropertyNameSyntax.

This will help us introduce the ComputedPropertyName concept in the future.

Conflicts:
	src/services/syntax/syntaxNodes.concrete.generated.ts
Add support for parsing computed property names.
Simplify code.
Removed duplicate diagnostic.
Merge pull request #1067 from Microsoft/deduplicateTypeNotAssignableMessage

Removed duplicate diagnostic message.
Merge pull request #1065 from Microsoft/shorthandProperties

Add support for parsing shorthand property assignments.
Address feedback
Merge branch 'master' into computedPropertyName