Summary

This PR parametrizes the Ast traits with a Language type and moves them to the rome_rowan crate so that they can be shared between rome_js_syntax and rome_css_syntax (and potential future crates).

Other changes:

• Renames the JS/CSS Syntax* aliases to JsSyntax* and CssSyntax. For example: type SyntaxNode = rome_rowan::SyntaxNode<JsLanguage> is now called JsSyntaxNode. I believe this helps understanding the difference between the different nodes and aligns the naming with the kind types (that are called JsSyntaxKind and CssSyntaxKind
• Moved most util methods to the SyntaxNode struct.
• Renamed cast to try_cast and move the SyntaxNodeExt::to to method to AstNode with the name cast.

Test Plan

cargo test