Until a better solution can be found for types that appear both in
request & response types and would otherwise require incoming types to
appear as fields of outgoing types.
Some types used for encryption related tasks need to be used across more
internal crates than expected, so a few have been moved and renamed for
clarity.
* Rename the key_algorithms module in ruma-identifiers-validation to crypto_algorithms
* Move ruma_events::Algorithm to ruma-identifiers-validation and rename it EventEncryptionAlgorithm
* Move DeviceKeys from ruma-client-api to ruma-common
At the same time, this commit makes `ServerName` a newtype around str so
other identifier types can borrow out their server name part as a
`&ServerName`. This technique works for `ServerName` because it keeps no
additional metadata. For the other identifier types to support being
created in borrowed form from a string slice, custom DSTs first have to
be added to Rust.
