PanelEditor: add data provider when switching from non data panel (#94220)

[everettbu]

Test for commit f32fe9a

[greptile-apps]

Greptile Summary

This PR adds proper data provider management when switching between panel types in the PanelEditor. When switching from a data-supporting panel to a non-data panel (skipDataQuery: true), it now properly cleans up the $data provider. When switching the other direction, it creates a new data provider using the last used datasource or falls back to the default datasource.

Key changes:

• Added cleanup logic to remove $data provider when switching to panels that skip data queries
• Added initialization logic to create $data provider when switching to panels that support data queries
• Enhanced test coverage to verify $data state is properly managed for both panel types
• Uses getLastUsedDatasourceFromStorage() and config.defaultDatasource for intelligent datasource selection

Confidence score: 4/5

• This PR is safe to merge with minor risk
• The implementation properly handles data provider lifecycle management when switching panel types. The logic is straightforward and well-tested. Only concern is potential null reference in dashboard UID access which should be addressed.
• Pay attention to PanelEditor.tsx line 212 for potential null reference handling

_{2 files reviewed, 1 comment}

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[greptile-apps]

logic: Consider using optional chaining here as getDashboardSceneFor(this).state.uid might be undefined:

Suggested change

	let ds = getLastUsedDatasourceFromStorage(getDashboardSceneFor(this).state.uid!)?.datasourceUid;
	if (!ds) {
	ds = config.defaultDatasource;
	let ds = getLastUsedDatasourceFromStorage(getDashboardSceneFor(this).state.uid)?.datasourceUid;

[everettbu]

Closing PR as part of cleanup