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>

sqlx-cli/src/database.rs

@@ -11,7 +11,7 @@ pub async fn create(connect_opts: &ConnectOpts) -> anyhow::Result<()> {
     let exists = crate::retry_connect_errors(connect_opts, Any::database_exists).await?;
 
     if !exists {
-        #[cfg(feature = "sqlite")]
+        #[cfg(feature = "_sqlite")]
         sqlx::sqlite::CREATE_DB_WAL.store(
             connect_opts.sqlite_create_db_wal,
             std::sync::atomic::Ordering::Release,

sqlx-cli/src/opt.rs

@@ -258,7 +258,7 @@ pub struct ConnectOpts {
     /// However, if your application sets a `journal_mode` on `SqliteConnectOptions` to something
     /// other than `Wal`, then it will have to take the database file out of WAL mode on connecting,
     /// which requires an exclusive lock and may return a `database is locked` (`SQLITE_BUSY`) error.
-    #[cfg(feature = "sqlite")]
+    #[cfg(feature = "_sqlite")]
     #[clap(long, action = clap::ArgAction::Set, default_value = "true")]
     pub sqlite_create_db_wal: bool,
 }