Show the map's credit where it can be seen

[octopranav]

What changes

• The problem. MapLibre draws its credit button and logo in the map's bottom corner. In the app that corner is under the sheet, so the map carried no visible credit.
• What is owed. OpenStreetMap's attribution guidelines ask for credit in a corner of the map, with the copyright page reachable. OpenFreeMap asks for "OpenFreeMap © OpenMapTiles Data from OpenStreetMap", with its three links.
• The fix. The library's credit and logo are turned off. PlaceMap now draws the credit its sources declare in the bottom-left corner of the uncovered map, above the sheet and clear of the button column (creditEnd). It sits on a plate of the surface colour so it reads over any basemap, each name is a link, and it is shown in full, as the site's maps show theirs (compact: false).
• Where the words come from. Credit.kt reads them from the style's sources (Source.getAttribution(), which the tiles' TileJSON supplies), shown once each. Until a source has declared a line, OpenFreeMap's own line stands in, word for word.

Checks

• :map:testDebugUnitTest: four new CreditTest cases.
  • a source's credit is shown
  • a credit two sources share is shown once
  • with no source declared, the provider's line stands in
  • the stand-in links OpenStreetMap to its copyright page
• Emulator:
  • Light and dark: the line sits in the bottom-left corner above the sheet, on one line, left of the buttons.
  • Tapping "OpenStreetMap" sent a VIEW intent for https://www.openstreetmap.org/… to Chrome.
  • Temporary build with the stand-in replaced by a marker: the line shown was still OpenFreeMap's, so it is read from the tiles. The build was reverted.