Write Ballerina Tests for scenarios that include language extensions APIs and Compiler APIs

[NipunaMarcus]

Description:
There are few example scenarios(Client-Generation, Ballerina-to-Swagger, Swagger-to-Ballerina, GRPC proto file gen) which generate a file using ballerina compiler plugin or an extension. It is hard to test these scenarios in Testerina as they include calling a API in ballerina side. We have to find a way to write these type of scenarios in Testerina or atleast discuss a resolution.