Support multiple .kt files for protocol types based on meta/type

[jangalinski]

Currently we create all types (data classes, value classes, enums and exceptions) contained in a protocol declaration in a single file (protocol-types.kt).
For better readability and to prepare separation of concerns for command- and query side, it would be nice to have multiple files (*-events.kt, *-commands.kt, *-queries.kt, ...).

This can be done by using a fileSpecList strategy and splitting the different types using the meta properties.