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

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

* s/Api/API/g

wsapi/websocket_handler.go

@@ -12,7 +12,7 @@ import (
 	"github.com/mattermost/mattermost-server/v6/shared/mlog"
 )
 
-func (api *API) ApiWebSocketHandler(wh func(*model.WebSocketRequest) (map[string]interface{}, *model.AppError)) webSocketHandler {
+func (api *API) APIWebSocketHandler(wh func(*model.WebSocketRequest) (map[string]interface{}, *model.AppError)) webSocketHandler {
 	return webSocketHandler{api.App, wh}
 }