Addition of long expression, index signature ad no functional elements

[Vishalk91-4]

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

• [x] N
• [ ] Y

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

grammar.js test/corpus/config.txt test/corpus/expr.txt test/corpus/literal.txt test/corpus/schema.txt test/corpus/type.txt src/grammar.json src/nodes-types.json

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

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

• [x] Added line breaks, comments of inline and block type
• [x] Added index signature and test cases
• [x] Added Test Cases for Index Expression and Documented String

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

• [x] 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 please review it