[parser] Parse a!?[0]

Fixes #41177.

Change-Id: I135f0b7aedbcb320ab0d1a1806b2ad3bedcda307
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/141886
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Reviewed-by: Johnni Winther <johnniwinther@google.com>
Commit-Queue: Jens Johansen <jensj@google.com>

https://dart.googlesource.com/sdk/+/43079207d4b6e5b7954b29cc43747bd7a6595176
diff --git a/commits.json b/commits.json
index 3666816..ea7cb51 100644
--- a/commits.json
+++ b/commits.json
@@ -1,5 +1,5 @@
 {
   "external/github.com/flutter/engine":"f7c6c6d92a126e5ad2a45bd28c6aa1ee1195a281",
   "external/github.com/flutter/flutter":"2a649b16e24fae5d7815e27fdeb9adcf2b621721",
-  "sdk":"0f89df0c00e7b09287f369920605785e55179a98"
+  "sdk":"43079207d4b6e5b7954b29cc43747bd7a6595176"
 }
\ No newline at end of file