fix(core): remove whitespaces in tree.json

tree.json can grow too large to be serialized, as detailed in #27261.
One reason why the file is very large is that the serialization uses
indentation level of 2. Removing the whitespace from serialization
will return a lot of spaces, and it is a very straightforward change.
This is OK to do because the file is not meant to be read by human
anyway. This PR implements the solution.

Ideally, in the future we should also make it possible to split
tree.json into multiple files or use the solution in
bmoffatt@91edfec,
to make it scalable. At that stage, it's also possible to turn
indentation space back to 2 (perhaps to aid debugging).

For now, however, this issue is blocking the deployment in our team,
and we really need this fix to continue.

Fixes #27261

Author: sorawee

packages/aws-cdk-lib/core/lib/private/tree-metadata.ts

@@ -77,7 +77,7 @@ export class TreeMetadata extends Construct {
       // tree.json
       if (key === 'parent') return undefined;
       return value;
-    }, 2), { encoding: 'utf-8' });
+    }), { encoding: 'utf-8' });
 
     builder.addArtifact('Tree', {
       type: ArtifactType.CDK_TREE,