Create GitLab MR before posting bot comment; improve composer error handling
### Problem/Motivation
Reorder operations so the GitLab MR is created and opened before the bot comment is posted, ensuring the comment's MR link resolves to the actual merge request even on brand-new issues. Improve composer error reporting and fix the normalization of Drupal paths that was broken in an earlier change.
### Work items
- Commit(s): [92ffb798a5](https://git.drupalcode.org/project/project_analysis/-/commit/92ffb798a588), [65b9906847](https://git.drupalcode.org/project/project_analysis/-/commit/65b9906847a0), [d6edc53a8a](https://git.drupalcode.org/project/project_analysis/-/commit/d6edc53a8aeb), [319d8393c8](https://git.drupalcode.org/project/project_analysis/-/commit/319d8393c8b2)
### Credit
- Implemented by: @bbrala
- Test-project feedback: @goba, @nicxvan, @wimleers, @rfay, @larowlan
---
*Filed retroactively as part of the Drupal 12 rector coverage effort. Closed as fixed; credit to be applied to the contributors listed above.*
*AI was used extensively to build this work and to file this issue. See [Dries Buytaert: AI-generated Rector rules for Drupal](https://dri.es/ai-generated-rector-rules-for-drupal) and [Björn Brala: Drupal Rector rules are config, not code. Mostly.](https://www.linkedin.com/pulse/drupal-rector-rules-config-code-mostly-bj%C3%B6rn-brala-vfpwe/).*
issue