v1.15.3 rebase

[smanders]

steps done locally

git switch xpro
git branch backup/xpro-before-squash
git reset --soft v1.15.3
git restore --staged .
git checkout -b v1.15.3_rebase
git add .devcontainer .gitmodules
cd .devcontainer
git describe --tags
git describe --tags | pbcopy
cd ..
git commit -m "externpro 25.07.17-3-ga5a7aaf"
git add .github/workflows/xp* .github/release-tag.json
git add CMakePresets* docker-compose.*
git add xprodeps.*
git commit -m "externpro init"
git add -p .github/workflows
git commit -m "upstream workflows, on: workflow_dispatch"
git add -p .gitignore
git commit -m "gitignore: add externpro ignores"
git add -p
git commit -m "CMakeLists.txt: xproinc, xpExternPackage"
git diff --exit-code xpv1.15.3.5 HEAD
git diff v1.15.3..xpv1.15.3.5 | git patch-id --stable; git diff v1.15.3..HEAD | git patch-id --stable
diff -u \\n<(git diff v1.15.3..xpv1.15.3.5) \\n<(git diff v1.15.3..HEAD)
<bump version in .github/release-tag.json>
git commit -m "release-tag: xpv1.15.3.6" .github/release-tag.json
git push cm v1.15.3_rebase 
diff -u \\n<(git diff v1.15.3..xpv1.15.3.5) \\n<(git diff v1.15.3..HEAD)
git push --force-with-lease cm xpro