Generate server-side responses into LSP.Messages.Server_Responses
package. Create LSP.Messages.Client_Responses for opposite
diresction.
We also change the method of reading responses - instead of using
'Input we use 'Read attribute and create response with correct
Is_Error discriminant before reading. This allow us inherit
'Read aspect for derived types.
The idea is to check encoders/decoders of LSP messages by converting
sample JSON files to Ada object, then converting it back and compare
result with origin JSON.
