[MM-37772] Idiomatic naming (URL, URI, API) (#18128)

* s/Url/URL/g & s/Uri/URI/g

* s/Api/API/g

api4/system_test.go

@@ -71,7 +71,7 @@ func TestGetPing(t *testing.T) {
 
 	th.TestForAllClients(t, func(t *testing.T, client *model.Client4) {
 		th.App.ReloadConfig()
-		resp, err := client.DoApiGet("/system/ping", "")
+		resp, err := client.DoAPIGet("/system/ping", "")
 		require.NoError(t, err)
 		require.Equal(t, http.StatusOK, resp.StatusCode)
 		respBytes, err := ioutil.ReadAll(resp.Body)
@@ -84,7 +84,7 @@ func TestGetPing(t *testing.T) {
 		defer os.Unsetenv("MM_FEATUREFLAGS_TESTFEATURE")
 		th.App.ReloadConfig()
 
-		resp, err = client.DoApiGet("/system/ping", "")
+		resp, err = client.DoAPIGet("/system/ping", "")
 		require.NoError(t, err)
 		require.Equal(t, http.StatusOK, resp.StatusCode)
 		respBytes, err = ioutil.ReadAll(resp.Body)
@@ -750,7 +750,7 @@ func TestPushNotificationAck(t *testing.T) {
 	defer th.TearDown()
 
 	t.Run("should return error when the ack body is not passed", func(t *testing.T) {
-		handler := api.ApiHandler(pushNotificationAck)
+		handler := api.APIHandler(pushNotificationAck)
 		resp := httptest.NewRecorder()
 		req := httptest.NewRequest("POST", "/api/v4/notifications/ack", nil)
 		req.Header.Set(model.HeaderAuth, "Bearer "+session.Token)
@@ -764,7 +764,7 @@ func TestPushNotificationAck(t *testing.T) {
 		privateChannel := th.CreateChannelWithClient(th.SystemAdminClient, model.ChannelTypePrivate)
 		privatePost := th.CreatePostWithClient(th.SystemAdminClient, privateChannel)
 
-		handler := api.ApiHandler(pushNotificationAck)
+		handler := api.APIHandler(pushNotificationAck)
 		resp := httptest.NewRecorder()
 		req := httptest.NewRequest("POST", "/api/v4/notifications/ack", nil)
 		req.Header.Set(model.HeaderAuth, "Bearer "+session.Token)