fix(spec2cdk): get tag gives null result in Java CDK (#29870)

### Issue # (if applicable)

Closes #29869

### Reason for this change

Without it, it breaks java users who rely on tagging name to generate resource id.

### Description of changes

Provide a default value using the initial `tagValue` users provide.

### Description of how you validated changes

Existing tests all pass. Essentially changing it back to the original state.

### Checklist
- [ ] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

tools/@aws-cdk/spec2cdk/lib/cdk/resource-decider.ts

@@ -153,15 +153,15 @@ export class ResourceDecider {
             summary: 'Tag Manager which manages the tags for this resource',
           },
         },
-        initializer: (_: Expression) =>
+        initializer: (props: Expression) =>
           new CDK_CORE.TagManager(
             this.tagManagerVariant(variant),
             expr.lit(this.resource.cloudFormationType),
-            expr.UNDEFINED,
+            $E(props)[originalName],
             expr.object({ tagPropertyName: expr.lit(originalName) }),
           ),
         cfnValueToRender: {
-          [originalName]: $this.tags.renderTags($this[rawTagsPropName]),
+          [originalName]: $this.tags.renderTags(),
         },
       },
       {