Fix render order of symbol layers for filled marker/filled line/arrow subsymbol

[nyalldawson]

If a filled marker/filled line/arrow line had eg a centroid fill marker in the subsymbol, this would always be rendered on top, regardless of the actual defined order

[github-actions]

🪟 Windows builds

Download Windows builds of this PR for testing.
Debug symbols for this build are available here.
(Built from commit dc57c94)

🪟 Windows Qt6 builds

Download Windows Qt6 builds of this PR for testing.
(Built from commit dc57c94)

[nirvn]

Nice, thanks for addressing this.

[qgis-bot]

The backport to release-3_40 failed:

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

stderr

error: could not apply 553c8e98412... Also fix render order for filled line
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/core/symbology/qgsmarkersymbollayer.cpp
Auto-merging src/core/symbology/qgsmarkersymbollayer.h
[backport-60575-to-release-3_40 ec225d09dd5] Fix render order of symbol layers for filled marker subsymbol
 Author: Nyall Dawson <[email protected]>
 Date: Thu Feb 13 13:22:53 2025 +1000
 6 files changed, 52 insertions(+)
 create mode 100644 tests/testdata/control_images/symbol_filledmarker/expected_filledmarker_centroid/expected_filledmarker_centroid.png
Auto-merging python/PyQt6/core/auto_generated/symbology/qgslinesymbollayer.sip.in
Auto-merging python/core/auto_generated/symbology/qgslinesymbollayer.sip.in
Auto-merging src/core/symbology/qgslinesymbollayer.cpp
Auto-merging tests/src/python/test_qgsfilledlinesymbollayer.py
CONFLICT (content): Merge conflict in tests/src/python/test_qgsfilledlinesymbollayer.py

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_40 release-3_40
# Navigate to the new working tree
cd .worktrees/backport-release-3_40
# Create a new branch
git switch --create backport-60575-to-release-3_40
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick 39f6824203b4654aa236ef46b212d7b823c8dd1b,553c8e984128bedca01ba460fe582ed2c162d328,fb6ba9289d62ca6768fd6a3c362cb4540c3f832a,dc57c94962302894ab1f4f618ccde58c07edd2be
# Push it to GitHub
git push --set-upstream origin backport-60575-to-release-3_40
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-release-3_40

Then, create a pull request where the base branch is release-3_40 and the compare/head branch is backport-60575-to-release-3_40.