[Bugfix] Read SLD TextSymbolizer PointPlacement for lines

[rldhont]

Description

For lines, if labeling palcement is horizontal, the TextSymbolizer will contain PointPlacement instead of LinePlacement.

It completes #34223

[qgis-bot]

The backport to release-3_10 failed:

The process 'git' failed with exit code 128

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-34441-to-release-3_10
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick 82324ece0c9da91e1b3b2663cd70b0c3a8951965
# Push it to GitHub
git push --set-upstream origin backport-34441-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-34441-to-release-3_10.