Support for Custom URI Schemes in OAuth2 Redirect URIs (#37356)

Fix #34349

By the way, remove `(ctx *APIContext) HasAPIError() ` and `(ctx
*APIContext) GetErrMsg()` because they do nothing, the error handling
has been done in API's middeware

The existing OAuth2 tests were not quite right, refactored them together

modules/validation/binding_test.go

@@ -27,7 +27,6 @@ type (
 	TestForm struct {
 		BranchName   string `form:"BranchName" binding:"GitRefName"`
 		URL          string `form:"ValidUrl" binding:"ValidUrl"`
-		URLs         string `form:"ValidUrls" binding:"ValidUrlList"`
 		GlobPattern  string `form:"GlobPattern" binding:"GlobPattern"`
 		RegexPattern string `form:"RegexPattern" binding:"RegexPattern"`
 	}