Add more methods to deal with blocks

[gisostallenberg]

Description

Add more methods to deal with blocks

• getVariablesWithoutBlocks - All variables except block macro's
• getBlocks - All block names
• keepBlock - Keep a blocks content without the macro around it

Fixes # (issue) See #2107

Checklist:

• [ ] I have run composer run-script check --timeout=0 and no errors were reported
• [ ] The new code is covered by unit tests (check build/coverage for coverage report)
• [ ] I have updated the documentation to describe the changes

[waltertamboer]

I see this PR is still in draft. Are you still working on this or can this be closed?