## Why this should be merged
The need for examples to be in `package rawdb_test` made it difficult to
test other code that relied on non-exported `rawdb` identifiers.
## How this works
1. Move all testable examples from `database.libevm_test.go` to
`examples.libevm_test.go` _without any change_.
2. Change `database.libevm_test.go` to be in `package rawdb` and extend
the `WithSkipFreezers()` test.
## How this was tested
No change at all to testable examples. The `WithSkipFreezers()` test now
touches both the happy and (specific) error paths to demonstrate exact
behaviour (under the old approach it could have just been that there was
no error, even without the option).
