Fix advanced digitizing floater not wide enough

[elpaso]

Fix #65171 by making sure most significant digits are always visible (cut decimals and UOM if necessary).

I preferred this to an arbitrary and most of the times
unnecessary enlargement of the floater.

[github-actions]

🪟 Windows Qt6 builds

Download Windows Qt6 builds of this PR for testing.
To execute locally, unzip the downloaded zip file and run bin\qgis-bin.exe in the extracted directory.
You might be prompted by Windows Defender click "Run anyway"
(Built from commit 85002cb)

🍎 MacOS Qt6 builds

Download MacOS Qt6 builds of this PR for testing.
This app is not notarized, run sudo xattr -d com.apple.quarantine /Applications/QGIS*.app to avoid the warning
(Built from commit 85002cb)

[qgis-bot]

The backport to queued_ltr_backports failed:

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

stderr

error: could not apply 85002cb0ab4... Fix advanced digitizing floater not wide enough
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/gui/qgsadvanceddigitizingfloater.cpp
CONFLICT (content): Merge conflict in src/gui/qgsadvanceddigitizingfloater.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-66663-to-queued_ltr_backports
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick 85002cb0ab40d60e594cdd4a0aab515814d6a231
# Push it to GitHub
git push --set-upstream origin backport-66663-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-66663-to-queued_ltr_backports.