refactor(postgres): split describe into resolve and explain

Author: CathalMullan

sqlx-postgres/src/connection/describe.rs renamed to sqlx-postgres/src/connection/explain.rs

@@ -23,9 +23,10 @@ use sqlx_core::sql_str::SqlSafeStr;
 
 pub use self::stream::PgStream;
 
-pub(crate) mod describe;
+mod explain;
 mod establish;
 mod executor;
+mod resolve;
 mod sasl;
 mod stream;
 mod tls;