Refactor tsi_ssl_credentials target. (#29443)
Refactor tsi_ssl_credentials target. (#29443)

* Refactor tsi_ssl_credentials target.
stanley-cheung/grpc,ejona86/grpc,vjpai/grpc,grpc/grpc,vjpai/grpc,vjpai/grpc,grpc/grpc,ctiller/grpc,grpc/grpc,vjpai/grpc,jtattermusch/grpc,jtattermusch/grpc,ejona86/grpc,stanley-cheung/grpc,ctiller/grpc,ctiller/grpc,ejona86/grpc,stanley-cheung/grpc,ctiller/grpc,grpc/grpc,jtattermusch/grpc,ctiller/grpc,stanley-cheung/grpc,ejona86/grpc,jtattermusch/grpc,jtattermusch/grpc,jtattermusch/grpc,ejona86/grpc,jtattermusch/grpc,ejona86/grpc,stanley-cheung/grpc,stanley-cheung/grpc,ejona86/grpc,grpc/grpc,stanley-cheung/grpc,ctiller/grpc,vjpai/grpc,vjpai/grpc,jtattermusch/grpc,grpc/grpc,ejona86/grpc,ctiller/grpc,ejona86/grpc,vjpai/grpc,grpc/grpc,ejona86/grpc,stanley-cheung/grpc,grpc/grpc,stanley-cheung/grpc,ctiller/grpc,stanley-cheung/grpc,jtattermusch/grpc,jtattermusch/grpc,vjpai/grpc,jtattermusch/grpc,ctiller/grpc,stanley-cheung/grpc,ctiller/grpc,ctiller/grpc,grpc/grpc,ejona86/grpc,grpc/grpc,stanley-cheung/grpc,vjpai/grpc,grpc/grpc,jtattermusch/grpc,vjpai/grpc,ctiller/grpc,vjpai/grpc,vjpai/grpc,ejona86/grpc,grpc/grpc