Improve parser

[DaniPopes]

This PR does 3 main things to the solang-parser crate:

1. adds documentation to all items
2. improves some logic in the parsing functions, like less allocations and some minor refactoring
3. most importantly, adds parse tree helpers (moving existing implementations):

• fmt: implements std::fmt::Display for all parse tree types
• loc, expanding on the CodeLocation traits:
  • implementations for all possible parse tree types
  • generic implementations for Vec, Option etc
  • renames the loc method to loc_opt on OptionalCodeLocation to avoid name collision
  • previously there were some standalone (not with the traits) methods on structs, these were moved to the trait implementations
• ord: implements std::cmp::{Ord, PartialOrd}
• helper methods on parse tree types; you can view them by looking for the impl blocks in pt

The massive diff in the lexer tests is just whitespace and renaming the fully qualified collect::<Vec<...>> to just Vec<_>

Some of these changes have been upstreamed from foundry-rs/foundry's forge-doc and forge-fmt.

BREAKING CHANGES:

• pt::OptionalCodeLocation::loc renamed to loc_opt
• pt::Level::to_string renamed to as_str
• lexer::Spanned<Token, Loc, Error> split into Spanned<'a> and Result<'a, T = Spanned<'a>, E = LexicalError>
• pt::UsingList's Error variant changed from tuple to unit (no more () at the end)

[seanyoung]

The new files need:

// SPDX-License-Identifier: Apache-2.0

on the first line, else CI will fail. Also note the clippy errors.

[xermicus]

Thanks for your contribution!

[seanyoung]

There is a lot of good stuff in this - very large - pull request, it is great, thank you very much!

So I only have one comment, please us let know what you think. Thanks for some quality code changes. 🙏

[seanyoung]

@DaniPopes thank you very much, great stuff! 🙏