Doc: Updates to gdalbuiltvrt docs

[dbaston]

Adds a note about the default value of cells not covered by a source (to -te) and does some general cleanup/formatting.

[rouault]

The backport to release/3.10 failed:

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

stderr

error: could not apply 1a33b14cd0... Docs: Edit style, formatting in gdalbuildvrt.rst
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 advice.mergeConflict false"

stdout

Auto-merging doc/source/programs/gdalbuildvrt.rst
[backport-11489-to-release/3.10 ab93909678] Docs: Clarify behavior of gdalbuildvrt -te when source extends beyond inputs.
 Author: Daniel Baston <[email protected]>
 Date: Thu Dec 12 21:25:01 2024 -0500
 1 file changed, 3 insertions(+)
Auto-merging doc/source/programs/gdalbuildvrt.rst
CONFLICT (content): Merge conflict in doc/source/programs/gdalbuildvrt.rst

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/3.10 release/3.10
# Navigate to the new working tree
cd .worktrees/backport-release/3.10
# Create a new branch
git switch --create backport-11489-to-release/3.10
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick 601c2b203920b30f6444b178e337d1736d02c814,1a33b14cd0d3abcc6682ad52e2bd88cdc3ffd147
# Push it to GitHub
git push --set-upstream origin backport-11489-to-release/3.10
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-release/3.10

Then, create a pull request where the base branch is release/3.10 and the compare/head branch is backport-11489-to-release/3.10.

[rouault]

601c2b2 backported to 3.10