refactor(parser): create lexer to hold lexing logic

[koladilip]

Description of the change

Create separate class for lexing
Refactor language spec for variables and functions.

Checklists

Development

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• The code changed/added as part of this pull request has been covered with tests
• All tests related to the changed code pass in development

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[github-actions]

Coverage report

St.❔	Category	Percentage	Covered / Total
🔴	Statements	0%	0/2332
🔴	Branches	0%	0/9
🔴	Functions	0%	0/9
🔴	Lines	0%	0/2332

Show new covered files 🐣

St.❔	File	Statements	Branches	Functions	Lines
🔴	constants.ts	0%	0%	0%	0%
🔴	errors.ts	0%	0%	0%	0%
🔴	lexer.ts	0%	0%	0%	0%

Test suite run success

1 tests passing in 1 suite.

Report generated by 🧪jest coverage report action from 5e605c9