babel-generator: Add TypeScript support (#5896)

* babel-generator: Add TypeScript support

* Remove type declarations; not published from babylon

* Remove TODOs

* Consistently use `this.word` for tokens that are words

packages/babel-generator/src/generators/tsFlowCommon.js

@@ -0,0 +1,38 @@
+export function TypeAnnotation(node) {
+  this.token(":");
+  this.space();
+  if (node.optional) this.token("?");
+  this.print(node.typeAnnotation, node);
+}
+
+export function TypeParameterInstantiation(node): void {
+  this.token("<");
+  this.printList(node.params, node, {});
+  this.token(">");
+}
+
+export { TypeParameterInstantiation as TypeParameterDeclaration };
+
+export function TypeParameter(node) {
+  this._variance(node);
+
+  this.word(node.name);
+
+  if (node.bound) {
+    this.print(node.bound, node);
+  }
+
+  if (node.constraint) {
+    this.space();
+    this.word("extends");
+    this.space();
+    this.print(node.constraint, node);
+  }
+
+  if (node.default) {
+    this.space();
+    this.token("=");
+    this.space();
+    this.print(node.default, node);
+  }
+}