fix(RevisionDataGridView): Update RowCount while loading

[mstv]

Proposed changes

• RevisionDataGridView: (Asynchronously) update RowCount also if DisplayedRowCount returns 0 yet
• BackgroundUpdater: Always cool down after performing the _operation

Screenshots

Before

revision grid may stay empty until "Loading" is hidden

After

RowCount is updated every 300 milliseconds

Test methodology

• manual

Merge strategy

I agree that the maintainer squash merge this PR (if the commit message is clear).

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✒️ I contribute this code under The Developer Certificate of Origin.

[mstv]

Other calls of SetRowCountAndSelectRowsIfReady - at least the one from UpdateGraphAsync - will be removed in a follow-up, or rather the entire function UpdateGraphAsync.

[gerhardol]

The changes are understandable, I would have preferred that the extra timer was not needed.

Other calls of SetRowCountAndSelectRowsIfReady - at least the one from UpdateGraphAsync - will be removed in a follow-up, or rather the entire function UpdateGraphAsync.

Can this remove the second timer?

[mstv]

I would have preferred that the extra timer was not needed.

Other calls of SetRowCountAndSelectRowsIfReady - at least the one from UpdateGraphAsync - will be removed in a follow-up, or rather the entire function UpdateGraphAsync.

Can this remove the second timer?

all done in #11719