Extract configuration fields from task to spec class (1/3)

[rougsig]

Background
To prevent eager task configuration for android, we need to know the list of output folders from generate proto task.

Changes
Extract all configuration fields from GenerateProtoTask to one GenerateProtoTaskSpec field.

Test plan
Green pipelines.

[rougsig]

note:
small part for fix for #643.

Second Part will be rewrite generateProtoTask {} to use spec directly without task proxy.
Third part will be use extracted values from task as sources for agp/other tasks.