SyntaxTree is !Send and !Sync in parser 0.7.1

[SimonSapin]

From @yanns in https://discord.com/channels/1022972389463687228/1117957327216201758/1163481102049083483, via #469 (comment):

Hi, when I try to upgrade apollo-parser from 0.6.1 to 0.7.1, I have an issue with some types that are not Sync anymore:

error[E0277]: `std::ptr::NonNull<rowan::cursor::NodeData>` cannot be shared between threads safely
   --> src/feature_toggle/plugin.rs:74:17
    |
74  | impl Plugin for FeatureTogglePlugin {
    |                 ^^^^^^^^^^^^^^^^^^^ `std::ptr::NonNull<rowan::cursor::NodeData>` cannot be shared between threads safely
    |
    = help: within `feature_toggle::plugin::FeatureTogglePlugin`, the trait `std::marker::Sync` is not implemented for `std::ptr::NonNull<rowan::cursor::NodeData>`
note: required because it appears within the type `SyntaxNode`
   --> /Users/yannsimon/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rowan-0.15.13/src/cursor.rs:146:12
    |
146 | pub struct SyntaxNode {
    |            ^^^^^^^^^^
note: required because it appears within the type `SyntaxNode<GraphQLLanguage>`
   --> /Users/yannsimon/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rowan-0.15.13/src/api.rs:16:12
    |
16  | pub struct SyntaxNode<L: Language> {
    |            ^^^^^^^^^^
note: required because it appears within the type `Document`
   --> /Users/yannsimon/.cargo/registry/src/index.crates.io-6f17d22bba15001f/apollo-parser-0.7.1/src/cst/generated/nodes.rs:19:12
    |
19  | pub struct Document {
    |            ^^^^^^^^
note: required because it appears within the type `PhantomData<Document>`
   --> /Users/yannsimon/.rustup/toolchains/stable-aarch64-apple-darwin/lib/rustlib/src/rust/library/core/src/marker.rs:789:12
    |
789 | pub struct PhantomData<T: ?Sized>;
    |            ^^^^^^^^^^^
note: required because it appears within the type `SyntaxTree`
   --> /Users/yannsimon/.cargo/registry/src/index.crates.io-6f17d22bba15001f/apollo-parser-0.7.1/src/parser/syntax_tree.rs:55:12
    |
55  | pub struct SyntaxTree<T: CstNode = cst::Document> {
    |            ^^^^^^^^^^

I can fix this one by removing SyntaxTree from the plugin and saving a Arc<String> that I parse each time. It's not the most efficient.

[yanns]

awesome thanks!