go/tools: add check for time formats with 2006-02-01

yyyy-dd-mm is a time format that isn't really used anywhere [1]. It is
much more likely that the user intended to use yyyy-mm-dd instead and
made a mistake. This happens quite often [2] because of the unusual way
to handle time formatting and parsing in Go. Since the mistake is Go
specific and happens so often a vet check will be useful.

1. https://stackoverflow.com/questions/2254014/are-there-locales-or-common-programs-that-use-yyyy-dd-mm-as-the-date-format
2. https://github.com/search?l=&p=1&q=%222006-02-01%22+language%3AGo&type=Code

Updates golang/go#48801

Change-Id: I20960c93710766f20a7df90873bff960dea41b28
GitHub-Last-Rev: 496b9917b5eda0525cb75d04a3487d174ccf8fea
GitHub-Pull-Request: golang/tools#342
Reviewed-on: https://go-review.googlesource.com/c/tools/+/354010
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Tim King <taking@google.com>
Run-TryBot: Tim King <taking@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>
diff --git a/internal/lsp/source/api_json.go b/internal/lsp/source/api_json.go
index 807f496..e20b8a6 100755
--- a/internal/lsp/source/api_json.go
+++ b/internal/lsp/source/api_json.go
@@ -379,6 +379,11 @@
 							Default: "true",
 						},
 						{
+							Name:    "\"timeformat\"",
+							Doc:     "check for calls of (time.Time).Format or time.Parse with 2006-02-01\n\nThe timeformat checker looks for time formats with the 2006-02-01 (yyyy-dd-mm)\nformat. Internationally, \"yyyy-dd-mm\" does not occur in common calendar date\nstandards, and so it is more likely that 2006-01-02 (yyyy-mm-dd) was intended.\n",
+							Default: "true",
+						},
+						{
 							Name:    "\"unmarshal\"",
 							Doc:     "report passing non-pointer or non-interface values to unmarshal\n\nThe unmarshal analysis reports calls to functions such as json.Unmarshal\nin which the argument type is not a pointer or an interface.",
 							Default: "true",
@@ -967,6 +972,11 @@
 			Default: true,
 		},
 		{
+			Name:    "timeformat",
+			Doc:     "check for calls of (time.Time).Format or time.Parse with 2006-02-01\n\nThe timeformat checker looks for time formats with the 2006-02-01 (yyyy-dd-mm)\nformat. Internationally, \"yyyy-dd-mm\" does not occur in common calendar date\nstandards, and so it is more likely that 2006-01-02 (yyyy-mm-dd) was intended.\n",
+			Default: true,
+		},
+		{
 			Name:    "unmarshal",
 			Doc:     "report passing non-pointer or non-interface values to unmarshal\n\nThe unmarshal analysis reports calls to functions such as json.Unmarshal\nin which the argument type is not a pointer or an interface.",
 			Default: true,