Replace "field formal" with "initializing formal" in diagnostic documentation

This appears to be the more widely used term for formal parameters of the
form `this.x`, and the docs ought to reflect common usage.

Also, fixes a typo in one other message.

Change-Id: I261d05e78f813db91a1df072bd72356a5e366226
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/228600
Reviewed-by: Samuel Rawlins <srawlins@google.com>
Commit-Queue: Brian Wilkerson <brianwilkerson@google.com>

https://dart.googlesource.com/sdk/+/3fbe18b612c57bc0c5288c59494ff51e9409bbf8
diff --git a/commits.json b/commits.json
index fd55544..013bf9c 100644
--- a/commits.json
+++ b/commits.json
@@ -1,5 +1,5 @@
 {
   "external/github.com/flutter/engine":"cef8bcede6399fc82343bd68d90427caf042b2be",
   "external/github.com/flutter/flutter":"5d5958f3588ee1ed25e31445d4b74b2a52c1025d",
-  "sdk":"3b736b846064295f08727b914b65561487a74540"
+  "sdk":"3fbe18b612c57bc0c5288c59494ff51e9409bbf8"
 }
\ No newline at end of file