Added Additional Schema, Mixin and Rule opeations

[Vishalk91-4]

1. Does this PR affect any open issues?(Y/N) and add issue references (e.g. "fix #123", "re #123".):

• N
• Y

re #2

2. What is the scope of this PR (e.g. component or file name):

gammar.js
schema.txt

3. Provide a description of the PR(e.g. more details, effects, motivations or doc link):

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Other

• Improved Code for Schema Statements
• Improved Code for Mixin Statements
• Improved Code for Rule Statements
• Added Test Cases for the above statements

4. Are there any breaking changes?(Y/N) and describe the breaking changes(e.g. more details, motivations or doc link):

• N
• Y

5. Are there test cases for these changes?(Y/N) select and add more details, references or doc links:

• Unit test
• Integration test
• Benchmark (add benchmark stats below)
• Manual test (add detailed scripts or steps below)
• Other

[Vishalk91-4]

@Peefy, could you review it

[Peefy]

Good Job! I will review it later.

[Peefy]

LGTM

[Peefy]

LGTM