Add a mosaic function

[tpoisot]

What the pull request does

Add a mosaic function to join multiple possibly overlapping layers

Type of change

Please indicate the relevant option(s)

• ❇️ New feature (non-breaking change which adds functionality)

Checklist

• The changes are documented
  • The docstrings of the different functions describe the arguments, purpose, and behavior
  • There are examples in the documentation website
• The changes are tested
• The changes do not modify the behavior of the previously existing functions
• The Project.toml field version has been updated

[mkborregaard]

He he, nice call.