Fix constant elements hoisted before declarator (#4804)

When multiple declarators are present in a declaration, we want to insert the constant element inside the declaration rather than placing it before because it may rely on a declarator inside that same declaration.

packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/dont-hoist-before-declaration/actual.js

@@ -0,0 +1,11 @@
+function render() {
+  const bar = "bar", renderFoo = () => <foo bar={bar} />;
+
+  return renderFoo();
+}
+
+function render() {
+  const bar = "bar", renderFoo = () => <foo bar={bar} baz={baz} />, baz = "baz";
+
+  return renderFoo();
+}

packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/dont-hoist-before-declaration/expected.js

@@ -0,0 +1,15 @@
+function render() {
+  const bar = "bar",
+        _ref = <foo bar={bar} />,
+        renderFoo = () => _ref;
+
+  return renderFoo();
+}
+
+function render() {
+  const bar = "bar",
+        renderFoo = () => <foo bar={bar} baz={baz} />,
+        baz = "baz";
+
+  return renderFoo();
+}