adds implementation of annotations constraint ISL 2.0

[desaikd]

Description of changes:

This PR adds implementation of annotations constraint ISL 2.0.

Grammar:

<ANNOTATIONS> ::= annotations: <ANNOTATIONS_MODIFIER>... [ <SYMBOL>... ]
                | annotations: <TYPE_ARGUMENT>

<ANNOTATIONS_MODIFIER> ::= required::
                         | closed::

Ion schema specification:

https://amazon-ion.github.io/ion-schema/docs/isl-2-0/spec#annotations

List of changes:

• adds support for standard and simple syntax for annotations constraint as per ISL 2.0
• adds enum IslAnnotationsConstraint which holds two variants for standard and simple syntax of annotations constraint
• adds Anotations2_0Constraint to handle ISL 2.0 related annotations validation based on a type reference

• adds unit tests for annotations constraint ISL 2.0

  By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.