Add general expresion context in raster temporal properties

[Djedouas]

Description

Add global contexts to start/end date expression in raster layer temporal properties "Fixed time range per band" mode.

As a result, variables like @layer_name can be used now.

---

Funded by CNES

[github-actions]

🪟 Windows builds

Download Windows builds of this PR for testing.
Debug symbols for this build are available here.
(Built from commit 49d7cf2)

🪟 Windows Qt6 builds

Download Windows Qt6 builds of this PR for testing.
(Built from commit 49d7cf2)

[troopa81]

Thanks, I was looking for that too!

[qgis-bot]

The backport to queued_ltr_backports failed:

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

stderr

error: could not apply 49d7cf2cc27... fix(raster-temporal-properties): add global contexts to start/end date expression
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 src/gui/raster/qgsrasterlayertemporalpropertieswidget.cpp
CONFLICT (content): Merge conflict in src/gui/raster/qgsrasterlayertemporalpropertieswidget.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-60144-to-queued_ltr_backports
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick 49d7cf2cc271dac0785f17ab20ce8674ed2a383d
# Push it to GitHub
git push --set-upstream origin backport-60144-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-60144-to-queued_ltr_backports.