Bugfix/missing peerdeps

[a-gagnon]

Add missing peerDependencies that are required at runtime by the map-layers package.
Besides type imports, anything that is used by the package should be a direct dependency, or be in both devDependency and peerDependency.

• Move some devDependencies to direct dependencies

Found the problem when adding the @itwin/map-layers package to my test-app. I didn't get a warning for missing peerDependency, but it complained about missing @itwin/map-layers-formats at build time.