Add tests for all supported languages

[AyanSinhaMahapatra]

Add tests for source symbol extraction in all supported languages:
For example, in tree-sitter here we have the following languages:
"Bash", "C", "C++", "Go", "Java", "JavaScript", "Python", "Rust"

We need to add unit tests for all these languages, and also have these supported languages in a supported language matrix in the README docs for easy access.