parse async closures

[m4rch3n1ng]

parse async closures. see reference

i just added it as an optional modifier to the (closure_expression), like with async functions, instead of as a seperate node like (async_block), but i can change that if you want me to.

the reference doesn't specify how static closures work, but in my testing rustc does not want to give an ast for async static move, but gives an ast for static async move.

diff for #229:

this is actually a pretty substantial diff wow

--- .tmp/list.txt	2025-03-03 17:25:16.906975980 +0100
+++ .tmp/list.txt.async-closures	2025-03-03 17:19:07.415680818 +0100
@@ -1,4 +1,3 @@
-tests/codegen/async-closure-debug.rs
 tests/codegen/dst-offset.rs
 tests/codegen/function-arguments.rs
 tests/codegen/sanitizer/cfi/emit-type-metadata-id-itanium-cxx-abi-user-defined-types.rs
@@ -12,13 +11,11 @@
 tests/crashes/104685.rs
 tests/crashes/116979.rs
 tests/crashes/123887.rs
-tests/debuginfo/coroutine-closure.rs
 tests/debuginfo/coroutine-locals.rs
 tests/debuginfo/coroutine-objects.rs
 tests/debuginfo/function-names.rs
 tests/debuginfo/issue-57822.rs
 tests/debuginfo/type-names.rs
-tests/mir-opt/async_closure_shims.rs
 tests/mir-opt/building/match/never_patterns.rs
 tests/mir-opt/coroutine_drop_cleanup.rs
 tests/mir-opt/coroutine_storage_dead_unwind.rs
@@ -51,24 +48,10 @@
 tests/ui/associated-types/default-associated-types.rs
 tests/ui/associated-types/issue-25339.rs
 tests/ui/associated-types/issue-32350.rs
-tests/ui/async-await/async-closures/call-once-deduction.rs
-tests/ui/async-await/async-closures/constrained-but-no-upvars-yet.rs
-tests/ui/async-await/async-closures/different-projection-lengths-for-different-upvars.rs
-tests/ui/async-await/async-closures/implements-fnmut.rs
-tests/ui/async-await/async-closures/inline-body.rs
-tests/ui/async-await/async-closures/mac-body.rs
-tests/ui/async-await/async-closures/moro-example.rs
-tests/ui/async-await/async-closures/no-borrow-from-env.rs
-tests/ui/async-await/async-closures/sig-from-bare-fn.rs
-tests/ui/async-await/async-closures/signature-deduction.rs
-tests/ui/async-await/async-closures/signature-inference-from-two-part-bound.rs
-tests/ui/async-await/async-closures/truncated-fields-when-imm.rs
-tests/ui/async-await/async-closures/validate-synthetic-body.rs
 tests/ui/async-await/async-fn/sugar.rs
 tests/ui/async-await/for-await-passthrough.rs
 tests/ui/async-await/for-await.rs
 tests/ui/async-await/issues/issue-65419/issue-65419-coroutine-resume-after-completion.rs
-tests/ui/async-await/no-params-non-move-async-closure.rs
 tests/ui/async-await/pin-ergonomics/sugar.rs
 tests/ui/async-await/return-type-notation/issue-110963-late.rs
 tests/ui/async-await/return-type-notation/normalizing-self-auto-trait-issue-109924.rs
@@ -235,7 +218,6 @@
 tests/ui/macros/user-defined-macro-rules.rs
 tests/ui/match/postfix-match/no-unused-parens.rs
 tests/ui/match/postfix-match/pf-match-chain.rs
-tests/ui/mir/issue-68841.rs
 tests/ui/nll/assign-while-to-immutable.rs
 tests/ui/nll/empty-type-predicate.rs
 tests/ui/nll/issue-112604-closure-output-normalize.rs
@@ -257,7 +239,6 @@
 tests/ui/rust-2018/uniform-paths/from-decl-macro.rs
 tests/ui/rust-2024/unsafe-extern-blocks/extern-items.rs
 tests/ui/rust-2024/unsafe-extern-blocks/safe-items.rs
-tests/ui/sanitizer/cfi/async-closures.rs
 tests/ui/simd/masked-load-store.rs
 tests/ui/sized/coinductive-1-gat.rs
 tests/ui/specialization/assoc-ty-graph-cycle.rs