SQL server browser/connections API optimisations

[nyalldawson]

Considerably lightens the load when browsing SQL Server connections via browser by avoiding excessive database queries

Fixes #31101

[github-actions]

🪟 Windows builds

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Debug symbols for this build are available here.
(Built from commit e58ea42)

🪟 Windows Qt6 builds

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(Built from commit e58ea42)

[nyalldawson]

I think this should be backported, given that it fixes #31101

[nyalldawson]

Approval in #60728

[qgis-bot]

The backport to queued_ltr_backports failed:

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

stderr

error: could not apply 19df56c51a1... [mssql] Don't query ALL tables to retrieve single table details
hint: After resolving the conflicts, mark them with
hint: "git add/rm <pathspec>", then run
hint: "git cherry-pick --continue".
hint: You can instead skip this commit with "git cherry-pick --skip".
hint: To abort and get back to the state before "git cherry-pick",
hint: run "git cherry-pick --abort".
hint: Disable this message with "git config set advice.mergeConflict false"

stdout

Auto-merging src/providers/mssql/qgsmssqlproviderconnection.cpp
CONFLICT (content): Merge conflict in src/providers/mssql/qgsmssqlproviderconnection.cpp

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-queued_ltr_backports queued_ltr_backports
# Navigate to the new working tree
cd .worktrees/backport-queued_ltr_backports
# Create a new branch
git switch --create backport-60680-to-queued_ltr_backports
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick 19df56c51a16dbb7791e069ea2b31ae9376015d8,f3c37f557fde81e009a24a8d5bacbcd2d6ea3096,555bbe3c44da8b63544ea5d01c802c109fe50a67,e58ea426666e874d31119cf603c9a58a8bff7bfc
# Push it to GitHub
git push --set-upstream origin backport-60680-to-queued_ltr_backports
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-queued_ltr_backports

Then, create a pull request where the base branch is queued_ltr_backports and the compare/head branch is backport-60680-to-queued_ltr_backports.