Datatable labelling rows (#1868)

* Renaming some component classes in DataTable

* Some more renaming of DataTable component classes

* Separate styling for fixed rows/columns from labels

* Highlight fixed rows/cols affected by colour differently

* Tweaking styles for fixed data in DataTable

* Update DataTable snapshots

* Add row label to Row metadata

* Wiring up some labelled row logic behind flags

* Renaming variable in DataTable

* Variable renaming in DataTable

* [no ci] Labelling rows progress

* Add RenderedRow abstraction to DataTable

* Computing label widths

* Use the Column object to represent row label column

* Ability to toggle row labels reactively

* Adjust width calculation for label widths

* Add DataTable.RowLabelSelected

* Posting the RowLabelClick message

* Hovering of row labels applies new style

* Remove a print

* Ensure horizontal scrolling with column cursor accounts for row label column

* Account for possible row labels in cell cursor horizontal scrolling

* Ensure cursor highlighting is correct on row label cells

* Document component class for DataTable label hover

* Test to ensure clicking row label emits correct event

* Add snapshot test for DataTable with fixed rows/cols and row labels

* Using pilot pause instead of wait_for_idle directly

* Update CHANGELOG

* Add a docstring

* Add a note to CHANGELOG.md about RowLabelSelected

tests/snapshot_tests/test_snapshots.py

@@ -108,6 +108,11 @@ def test_datatable_sort_multikey(snap_compare):
     assert snap_compare(SNAPSHOT_APPS_DIR / "data_table_sort.py", press=press)
 
 
+def test_datatable_labels_and_fixed_data(snap_compare):
+    # Ensure that we render correctly when there are fixed rows/cols and labels.
+    assert snap_compare(SNAPSHOT_APPS_DIR / "data_table_row_labels.py")
+
+
 def test_footer_render(snap_compare):
     assert snap_compare(WIDGET_EXAMPLES_DIR / "footer.py")