Loading indicator (#2018)

* loading indicator and tests

* docs

* snapshot

* remove snapshot

* remove debug main [skip ci]

* changelog [skip ci]

* make start time private

docs/widgets/loading_indicator.md

@@ -0,0 +1,24 @@
+# LoadingIndicator
+
+Displays pulsating dots to indicate when data is being loaded.
+
+- [ ] Focusable
+- [ ] Container
+
+
+=== "Output"
+
+    ```{.textual path="docs/examples/widgets/loading_indicator.py"}
+    ```
+
+=== "loading_indicator.py"
+
+    ```python
+    --8<-- "docs/examples/widgets/loading_indicator.py"
+    ```
+
+
+
+## See Also
+
+* [LoadingIndicator](../api/loading_indicator.md) code reference