Look for package name in `[extras]` for Preferences (#43361)
* Look for package name in `[extras]`
When Preferences.jl set's a preferences in a non-top-level package,
it adds that package to the `[extras]` entries in the project path.
Package loading should have used thhose entries to map the module uuid
to the key name in the Preferences.toml
Fixes https://github.com/JuliaPackaging/Preferences.jl/issues/24
Co-authored-by: Elliot Saba <staticfloat@gmail.com>
