fix: improve addChild and path performance (#1891)

Improve the performance of the `constructs` library by removing several branches in the library's hot paths and switching to some more performant operations.

On my laptop, the benchmark I used (shared in a gist [here](https://gist.github.com/Chriscbr/fa69e5f7f35d5aa4dc312dd7025952b1)) takes about 5.0-5.3 seconds with the old version of constructs, and about 1.1-1.2 seconds with the new version of constructs.

Misc:
- Removed an unused file in the `test` folder.
- Added some files to `npmignore` to reduce the package's npm footprint.

.projenrc.ts

@@ -81,5 +81,6 @@ project.buildWorkflow?.addPostBuildJobCommands(
   { checkoutRepo: true },
 );
 
+project.npmignore?.exclude('/scripts/', '.projenrc.ts');
 
 project.synth();

src/construct.ts

@@ -77,7 +77,12 @@ export class Node {
    * Components are separated by '/'.
    */
   public get path(): string {
-    const components = this.scopes.filter(c => c.node.id).map(c => c.node.id);
+    const components = [];
+    for (const scope of this.scopes) {
+      if (scope.node.id) {
+        components.push(scope.node.id);
+      }
+    }
     return components.join(Node.PATH_SEP);
   }
 
@@ -417,21 +422,13 @@ export class Node {
       throw new Error(`Cannot add children to "${this.path}" during synthesis`);
     }
 
-    if (childName in this._children) {
+    if (this._children[childName]) {
       const name = this.id ?? '';
       const typeName = this.host.constructor.name;
       throw new Error(`There is already a Construct with name '${childName}' in ${typeName}${name.length > 0 ? ' [' + name + ']' : ''}`);
     }
 
-    if (!childName && this.id) {
-      throw new Error(`cannot add a nameless construct to the named scope: ${this.path}`);
-    }
-
     this._children[childName] = child;
-
-    if (Object.keys(this._children).length > 1 && Object.keys(this._children).filter(x => !x).length > 0) {
-      throw new Error('only a single construct is allowed in a scope if it has an empty name');
-    }
   }
 }