Add a "sqlite-unbundled" feature that dynamically links to system libsqlite3.so library (#3507)

* Add a "sqlite-unbundled" feature that dynamically links to system libsqlite3.so library

* update README abouot the newly-added `sqlite-unbundled` feature

* Update README.md to make it clear with bulleted list

Co-authored-by: Austin Bonander <austin.bonander@gmail.com>

* more cfg feature updates

Co-authored-by: Austin Bonander <austin.bonander@gmail.com>

* update documentation in sqlx-sqlx/src/lib.rs too

and also mention possible build time increasement.

* cargo fmt

* Add "sqlite-unbundled" feature to sqlx-cli

* Add sqlite-unbundled to gituhb actions tests

* cfg(feature = "sqlite") => cfg(any(feature = "sqlite", feature = "sqlite-unbundled"))

* fix

* CI: make sqlite-unbundled tests workaround required-features

by duplicating the relevant test section

* use an internal "_sqlite" feature to do the conditional compilation

---------

Co-authored-by: Austin Bonander <austin.bonander@gmail.com>

src/any/mod.rs

@@ -41,7 +41,7 @@ pub fn install_default_drivers() {
             sqlx_mysql::any::DRIVER,
             #[cfg(feature = "postgres")]
             sqlx_postgres::any::DRIVER,
-            #[cfg(feature = "sqlite")]
+            #[cfg(feature = "_sqlite")]
             sqlx_sqlite::any::DRIVER,
         ])
         .expect("non-default drivers already installed")

src/lib.rs

@@ -44,8 +44,8 @@ pub use sqlx_mysql::{self as mysql, MySql, MySqlConnection, MySqlExecutor, MySql
 #[doc(inline)]
 pub use sqlx_postgres::{self as postgres, PgConnection, PgExecutor, PgPool, Postgres};
 
-#[cfg(feature = "sqlite")]
-#[cfg_attr(docsrs, doc(cfg(feature = "sqlite")))]
+#[cfg(feature = "_sqlite")]
+#[cfg_attr(docsrs, doc(cfg(feature = "_sqlite")))]
 #[doc(inline)]
 pub use sqlx_sqlite::{self as sqlite, Sqlite, SqliteConnection, SqliteExecutor, SqlitePool};