Merge 'bindings/javascript: Add source property to Statement' from Anton Harniakou

Let's you get the source string that was used to create the prepared
statement.

Reviewed-by: Diego Reis (@el-yawd)

Closes #1670

bindings/javascript/__test__/better-sqlite3.spec.mjs

@@ -214,6 +214,12 @@ test("Test Statement.database gets the database object", async t => {
   t.is(stmt.database, db);
 });
 
+test("Test Statement.source", async t => {
+  const [db] = await connect(":memory:");
+  let sql = "CREATE TABLE t (id int)";
+  let stmt = db.prepare(sql);
+  t.is(stmt.source, sql);
+});
 
 const connect = async (path) => {
   const db = new Database(path);

bindings/javascript/__test__/limbo.spec.mjs

@@ -215,6 +215,13 @@ test("Test Statement.database gets the database object", async t => {
   t.is(stmt.database, db);
 });
 
+test("Test Statement.source", async t => {
+  const [db] = await connect(":memory:");
+  let sql = "CREATE TABLE t (id int)";
+  let stmt = db.prepare(sql);
+  t.is(stmt.source, sql);
+});
+
 const connect = async (path) => {
   const db = new Database(path);
   return [db];

bindings/javascript/wrapper.js

@@ -178,10 +178,18 @@ class Statement {
     return this;
   }
 
+  get source() {
+    return this.stmt.source;
+  }
+
   get reader() {
     throw new Error("not implemented");
   }
 
+  get source() {
+    return this.stmt.source;
+  }
+
   get database() {
     return this.db;
   }