Refresh snapping index on vector data provider notify

[troopa81]

Description

Fixes #40720

When provider raise a notify message (PostGres PG_NOTIFY for instance), we have to trigger a repaint and fire a dataChanged signal so the snapping index is updated.

[nyalldawson]

@OccamLabRazor Just a friendly warning -- please moderate the tone of your comments on this tracker in future. This is our workplace, and we expect you to extend the same politeness and courtesy to @troopa81 as you'd expect from him in YOUR place of work. 👍

[elpaso]

@troopa81, let's be honest, your pull request does not solve the issue #40720.(The issue #40720 must be closed as it duplicates the problem described in #31251.)

No, they are not duplicates because the datasource is different, we do have a way to send notifications from a PG server to listening clients while there is no way for a WFS server to notify its clients.

IIRC there is a LOCK feature in WFS specs but I'm not aware of any client implementing it, it would be something different than notifications though.

[github-actions]

The backport to release-3_16 failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-release-3_16 release-3_16
# Navigate to the new working tree
cd .worktrees/backport-release-3_16
# Create a new branch
git switch --create backport-41357-to-release-3_16
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick --mainline 1 92fc1a7742a6b2ff35406daa40c663344a50236c
# Push it to GitHub
git push --set-upstream origin backport-41357-to-release-3_16
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-release-3_16

Then, create a pull request where the base branch is release-3_16 and the compare/head branch is backport-41357-to-release-3_16.