fix(create): show template selection before editor for -d- flag

Fix issue where using -d- flag in create commands would open an empty editor before showing template selection. Now the flow is:

1. Show template selection first
2. Open editor with selected template pre-filled

Changes:

• Add HandleDescriptionEditor helper in cmdutils for consistent -d- handling
• Extract template selection logic into command-specific helpers
• Apply fix to mr create, issue create, snippet create, and project create
• Remove code duplication (~40 lines in mr create, ~20 in issue create)

Closes #8181 (closed)