Only build libfwupdplugin source files once; we were only using one
non-exported symbol and so move that to the exported map so we can just link
the library in the self tests.
We now have two plugins getting the ESP values, and we only allow hardcoding
the ESP in uefi_capsule.conf.
Make all this a lot simpler by moving the ESP+BDP code to `FuContext`, which
also means we can handle the override (via the config file) in the engine,
and the override (in the command line tools) using the same mechanism.
Also, automate the migration of the `OverrideESPMountPoint` -> `EspLocation`
when loading the engine.
Fixes https://github.com/fwupd/fwupd/issues/5042
The end year is legally and functionally redundant, and more importantly causes
cherry-pick conflicts when trying to maintain old branches. Use git for history.
