Improve oauth2 client "preferred username field" logic and the error handling (#30622)

Follow #30454
And fix #24957

When using "preferred_username", if no such field,
`extractUserNameFromOAuth2` (old `getUserName`) shouldn't return an
error. All other USERNAME options do not return such error.

And fine tune some logic and error messages, make code more stable and
more friendly to end users.

models/user/user_test.go

@@ -506,15 +506,16 @@ func Test_NormalizeUserFromEmail(t *testing.T) {
 		Expected          string
 		IsNormalizedValid bool
 	}{
-		{"test", "test", true},
+		{"name@example.com", "name", true},
+		{"test'`´name", "testname", true},
 		{"Sinéad.O'Connor", "Sinead.OConnor", true},
 		{"Æsir", "AEsir", true},
-		// \u00e9\u0065\u0301
-		{"éé", "ee", true},
+		{"éé", "ee", true}, // \u00e9\u0065\u0301
 		{"Awareness Hub", "Awareness-Hub", true},
 		{"double__underscore", "double__underscore", false}, // We should consider squashing double non-alpha characters
 		{".bad.", ".bad.", false},
 		{"new😀user", "new😀user", false}, // No plans to support
+		{`"quoted"`, `"quoted"`, false}, // No plans to support
 	}
 	for _, testCase := range testCases {
 		normalizedName, err := user_model.NormalizeUserName(testCase.Input)