Adding Grammer

[Daksh-10]

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

• N
• Y

#8

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

./grammar.js

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

I will be adding more syntax changes related to 'expressions' in KCL. In this PR, I improved assignment statement and syntax for '?' operator.

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

[Peefy]

Hello.

Please not use the fix message in the PR description and it will lead to the PR be closed.

Please fix CI.

[Daksh-10]

Hey @Peefy , there are lots of error tokens which gives a lot of ways to improve the grammar.js ( also as @Vishalk91-4 mentioned), I will also try to remove those error tokens :)