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
1 file changed
tree: a3561370cc188e25b56e2611b41ae5db41e234ad
  1. commits.json