gopls/internal/analysis/yield: analyzer for iterator (yield) mistakes

This analyzer detects failure to check the result of a call to
yield (which can cause a range loop to run beyond the sequence,
leading to a panic).

It is not always a mistake to ignore the
result of a call to yield; it depends on whether control can
reach another call to yield without checking that the first
call returned true. Consequently, this analyzer uses SSA
for control flow analysis.

We plan to add this analyzer to gopls before we promote it to vet.

+ test, relnote

Fixes golang/go#65795

Change-Id: I75fa272e2f546be0c2acb10a1978c82bc19db5bd
Reviewed-on: https://go-review.googlesource.com/c/tools/+/609617
Auto-Submit: Alan Donovan <adonovan@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>
Commit-Queue: Alan Donovan <adonovan@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

Author: adonovan

gopls/internal/doc/api.json

@@ -1353,4 +1353,5 @@
 			"Default": false
 		}
 	]
-}
+}
+