Add Migrator::with_migrations() constructor (#4020)

* Add the helper function with_migrations() to Migrator.

* cargo fmt

* cargo fmt

* cargo fmt

* Improve comments.

sqlx-core/src/migrate/migrator.rs

@@ -69,6 +69,32 @@ impl Migrator {
         })
     }
 
+    /// Creates a new instance with the given migrations.
+    ///
+    ///
+    /// # Examples
+    ///
+    /// ```rust,no_run
+    /// use sqlx::{ SqlSafeStr, migrate::{Migration, MigrationType::*, Migrator}};
+    ///
+    /// // Define your migrations.
+    /// // You can also use include_str!("./xxx.sql") instead of hard-coded SQL statements.
+    /// let migrations = vec![
+    ///     Migration::new(1, "user".into(), ReversibleUp, "create table uesrs ( ... )".into_sql_str(), false),
+    ///     Migration::new(2, "post".into(), ReversibleUp, "create table posts ( ... )".into_sql_str(), false),
+    ///     // add more...
+    ///  ];
+    ///  let m = Migrator::with_migrations(migrations);
+    /// ```
+    pub fn with_migrations(mut migrations: Vec<Migration>) -> Self {
+        // Ensure that we are sorted by version in ascending order.
+        migrations.sort_by_key(|m| m.version);
+        Self {
+            migrations: Cow::Owned(migrations),
+            ..Self::DEFAULT
+        }
+    }
+
     /// Override the name of the table used to track executed migrations.
     ///
     /// May be schema-qualified and/or contain quotes. Defaults to `_sqlx_migrations`.