DEV: Add converter framework for migrations-tooling (#28540)

* Updates GitHub Actions
* Switches from `bundler/inline` to an optional group in the `Gemfile` because the previous solution didn't work well with rspec
* Adds the converter framework and tests
* Allows loading private converters (see README)
* Switches from multiple CLI tools to a single CLI
* Makes DB connections reusable and adds a new abstraction for the `IntermediateDB`
* `IntermediateDB` acts as an interface for IPC calls when a converter steps runs in parallel (forks). Only the main process writes to the DB.
* Includes a simple example implementation of a converter for now.

migrations/lib/database/migrator.rb

@@ -0,0 +1,82 @@
+# frozen_string_literal: true
+
+module Migrations::Database
+  class Migrator
+    def initialize(db_path)
+      @db_path = db_path
+      @db = nil
+    end
+
+    def migrate(migrations_path)
+      @migrations_path = migrations_path
+      @db = Connection.open_database(path: @db_path)
+
+      if new_database?
+        create_schema_migrations_table
+        performed_migrations = Set.new
+      else
+        performed_migrations = find_performed_migrations
+      end
+
+      migrate_from_path(@migrations_path, performed_migrations)
+
+      @db.close
+    end
+
+    def reset!
+      [@db_path, "#{@db_path}-wal", "#{@db_path}-shm"].each do |path|
+        FileUtils.remove_file(path, force: true) if File.exist?(path)
+      end
+    end
+
+    private
+
+    def new_database?
+      @db.query_single_splat(<<~SQL) == 0
+        SELECT COUNT(*)
+        FROM sqlite_schema
+        WHERE type = 'table' AND name = 'schema_migrations'
+      SQL
+    end
+
+    def find_performed_migrations
+      @db.query_splat(<<~SQL).to_set
+        SELECT path
+        FROM schema_migrations
+      SQL
+    end
+
+    def create_schema_migrations_table
+      @db.execute(<<~SQL)
+        CREATE TABLE schema_migrations
+        (
+            path       TEXT     NOT NULL PRIMARY KEY,
+            created_at DATETIME NOT NULL,
+            sql_hash   TEXT     NOT NULL
+        );
+      SQL
+    end
+
+    def migrate_from_path(migration_path, performed_migrations)
+      file_pattern = File.join(migration_path, "*.sql")
+      root_path = @migrations_path || ::Migrations.root_path
+
+      Dir[file_pattern].sort.each do |path|
+        relative_path = Pathname(path).relative_path_from(root_path).to_s
+
+        if performed_migrations.exclude?(relative_path)
+          sql = File.read(path)
+          sql_hash = Digest::SHA1.hexdigest(sql)
+
+          @db.transaction do
+            @db.execute(sql)
+            @db.execute(<<~SQL, path: relative_path, sql_hash: sql_hash)
+              INSERT INTO schema_migrations (path, created_at, sql_hash)
+              VALUES (:path, datetime('now'), :sql_hash)
+            SQL
+          end
+        end
+      end
+    end
+  end
+end