Fixes to Map plotting in user guide

[ayshih]

• Figures with multiple subplots were given insufficient size to lay out properly
• Axes were being grabbed as non-WCSAxes axes (i.e., no projection keyword)

[ghost]

Thanks for the pull request @ayshih! Everything looks great!

[backporting]

The backport to 1.0 failed:

Commits ["a8030bc501942458d6a516c0c85401d72a237040","b82814c94716d10e465b2b2f49f281191c9b649e"] could not be cherry-picked on top of 1.0

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub.
git fetch
# Create new working tree.
git worktree add .worktrees/backport 1.0
# Navigate to the new directory.
cd .worktrees/backport
# Cherry-pick all the commits of this pull request and resolve the likely conflicts.
git cherry-pick a8030bc501942458d6a516c0c85401d72a237040 b82814c94716d10e465b2b2f49f281191c9b649e
# Create a new branch with these backported commits.
git checkout -b backport-3454-to-1.0
# Push it to GitHub.
git push --set-upstream origin backport-3454-to-1.0
# Go back to the original working tree.
cd ../..
# Delete the working tree.
git worktree remove .worktrees/backport

Then, create a pull request where the base branch is 1.0 and the compare/head branch is backport-3454-to-1.0.

[ayshih]

Backport needs #3453 to be merged first