feat: add XcodeGen manager for Swift package dependencies in project.yml files

[stefanceriu]

Changes

This PR adds support for XcodeGen and updating dependencies within project.yml files.
It's based on the discussion from #20504

While I have mostly vibecoded this and I don't really know what I'm doing the code does make sense to me, especially the fixtures and unit tests.

In order to make sure it works I set up my local environment, ran the unit tests and then ran it on top of a public repository.
The results seem to be correct:

INFO: Repository started (repository=element-hq/element-x-ios)

"renovateVersion": "0.0.0-semantic-release"
 INFO: Dependency extraction complete (repository=element-hq/element-x-ios, baseBranch=develop)
       "stats": {
         "managers": {
           "cocoapods": {"fileCount": 1, "depCount": 1},
           "github-actions": {"fileCount": 15, "depCount": 57},
           "swift": {"fileCount": 1, "depCount": 4},
           "xcodegen": {"fileCount": 1, "depCount": 28}
         },
         "total": {"fileCount": 18, "depCount": 90}
       }
 INFO: DRY-RUN: Would commit files to branch renovate/asyncalgorithms-1.x (repository=element-hq/element-x-ios, branch=renovate/asyncalgorithms-1.x)
 INFO: DRY-RUN: Would commit files to branch renovate/lrucache-1.x (repository=element-hq/element-x-ios, branch=renovate/lrucache-1.x)
 INFO: DRY-RUN: Would commit files to branch renovate/snapshottesting-1.x (repository=element-hq/element-x-ios, branch=renovate/snapshottesting-1.x)
 INFO: DRY-RUN: Would commit files to branch renovate/swiftsoup-2.x (repository=element-hq/element-x-ios, branch=renovate/swiftsoup-2.x)
 INFO: DRY-RUN: Would commit files to branch renovate/swiftstate-6.x (repository=element-hq/element-x-ios, branch=renovate/swiftstate-6.x)
 INFO: DRY-RUN: Would commit files to branch renovate/analyticsevents-0.x (repository=element-hq/element-x-ios, branch=renovate/analyticsevents-0.x)
 INFO: DRY-RUN: Would commit files to branch renovate/collections-1.x (repository=element-hq/element-x-ios, branch=renovate/collections-1.x)
 INFO: DRY-RUN: Would commit files to branch renovate/devicekit-5.x (repository=element-hq/element-x-ios, branch=renovate/devicekit-5.x)
 INFO: DRY-RUN: Would commit files to branch renovate/dswaveformimage-14.x (repository=element-hq/element-x-ios, branch=renovate/dswaveformimage-14.x)
 INFO: DRY-RUN: Would commit files to branch renovate/kingfisher-8.x (repository=element-hq/element-x-ios, branch=renovate/kingfisher-8.x)
 INFO: DRY-RUN: Would commit files to branch renovate/maplibre-6.x (repository=element-hq/element-x-ios, branch=renovate/maplibre-6.x)
 INFO: DRY-RUN: Would commit files to branch renovate/posthog-3.x (repository=element-hq/element-x-ios, branch=renovate/posthog-3.x)
 INFO: DRY-RUN: Would commit files to branch renovate/sentry-9.x (repository=element-hq/element-x-ios, branch=renovate/sentry-9.x)
 INFO: DRY-RUN: Would ensure Dependency Dashboard (repository=element-hq/element-x-ios)
       "title": "Dependency Dashboard"
 INFO: DRY-RUN: Would save repository cache. (repository=element-hq/element-x-ios)
 INFO: Repository finished (repository=element-hq/element-x-ios)
       "cloned": true,
       "durationMs": 93030,
       "result": "done",
       "status": "activated",
       "enabled": true,
       "onboarded": true
 INFO: Renovate was run at log level "info". Set LOG_LEVEL=debug in environment variables to see extended debug logs.

I'm perfectly happy to follow your lead on this and make all the changes necessary to push it over the line.

Thank you, and thank you for Renovate! 🙏

Context

Please select one of the following:

• This closes an existing Issue, Closes: feat: Support XcodeGen #20504
• This doesn't close an Issue, but I accept the risk that this PR may be closed if maintainers disagree with its opening or implementation

AI assistance disclosure

Did you use AI tools to create any part of this pull request?

Please select one option and, if yes, briefly describe how AI was used (e.g., code, tests, docs) and which tool(s) you used.

• No — I did not use AI for this contribution.
• Yes — minimal assistance (e.g., IDE autocomplete, small code completions, grammar fixes).
• Yes — substantive assistance (AI-generated non‑trivial portions of code, tests, or documentation).
• Yes — other (please describe):

Documentation (please check one with an [x])

• I have updated the documentation, or
• No documentation update is required

How I've tested my work (please select one)

I have verified these changes via:

• Code inspection only, or
• Newly added/modified unit tests, or
• No unit tests, but ran on a real repository, or
• Both unit tests + ran on a real repository

The public repository: https://github.com/element-hq/element-x-ios