migrate to syn 2

[B-Reif]

Updates syn version to "2" and updates usage.

Closes #36.

[B-Reif]

It looks like the failing tests are being compared to older .stderr files which contain errors related to deriving ShaderType:

Currently in invalid_align_attr.stderr:

error: expected attribute arguments in parentheses: #[align(...)]
 --> tests/compile_fail/invalid_align_attr.rs:5:10
  |
5 | #[derive(ShaderType)]
  |          ^^^^^^^^^^
  |
  = note: this error originates in the derive macro `ShaderType` (in Nightly builds, run with -Z macro-backtrace for more info)

This error isn't getting thrown in the new test result, which seems like the correct behavior? Let me know if anything needs to change here.

[teoxoy]

Thank you for the PR!

We shouldn't have to update the expected error files; we seem to lose the span info now.

[B-Reif]

Having some trouble compiling on my machine now, will resume fixing this later

[teoxoy]

@B-Reif I ended up fixing the remaining issues since I wanted to release a new major version with the upgrade to syn2 included.