Split `boa_tester` into crates about boa

[jedel1043]

@PawelJastrzebski Thank you for the help! Yeah, that was mostly the idea: separate the test262 parser from the main program. Though, I'd recommend also including the git module inside test262_parser, maybe with some interface to be able to either download the repo or pass a manual path to a valid test262 directory.

[PawelJastrzebski]

Hi, I would like to contribute. Could you tell me if I'm going in the right direction?

I'm not sure if I'm understanding use case for this new crate, you want to extract all parsing logic from boa_tester to another crate so extraction/parsing logic could be reused. I'm not sure if I understand "extraction part" correctly.

test262-parser (todo typo) representing new crate