test: add MapLibre unit tests

[JamesLMilner]

Description of Changes

Adds unit tests for the MapLibre adapter. These are currently entirely based on the MapboxGL adapter tests as the API is still identical.

Link to Issue

No issue

PR Checklist

• [x] The PR title follows the conventional commit standard
• [ ] There is a associated GitHub issue
• [x] If I have added significant code changes, there are relevant tests
• [ ] If there are behaviour changes these are documented