Add QoL API for using BaseBackend/BackendCompatible

[ivanbakel]

withBaseBackend and withCompatibleBackend are simple wrappers for withReaderT that use the appropriate read-transforming function from their respective instances.

Also dogfoods these functions into the codebase.

Before submitting your PR, check that you've:

• Documented new APIs with Haddock markup
• Added @since declarations to the Haddock

After submitting your PR:

• Update the Changelog.md file with a link to your PR
• Bumped the version number if there isn't an (unreleased) on the Changelog
• Check that CI passes (or if it fails, for reasons unrelated to your change, like CI timeouts)

[parsonsmatt]

This is awesome, thanks!