Rename delegate to delegateNode

`SwipeToSceneRootNode` extends `DelegatingNode`, which contains an
internal variable named `delegate`. Rename this variable in the child
class.

This CL is motivated by fixes for missing kotlin xrefs in f/b/packages/SystemUI.
Android uses kotlinc < 2, while the google3 indexer ues kotlinc > 2.
Versions > 2 are more strict about changing the access privilege of
variables in child classes. At ToT, we get the following compilation
error during kotlinc in google3 indexer.
```
cannot weaken access privilege 'internal' for 'delegate' in 'DelegatingNode'
```

Test: m PlatformComposeSceneTransitionLayout # builds fine
Test: XREF_CORPUS=googleplex-android.googlesource.com/platform/superproject/main//main m out/soong/.intermediates/frameworks/base/packages/SystemUI/compose/scene/PlatformComposeSceneTransitionLayout/android_common/kotlin/PlatformComposeSceneTransitionLayout.kzip
Test: Ran the kotlin indexer locally on this kzip file using go/kythe-git-local-run#indexing-to-local-xrefs-server

Bug: 372675133
Flag: EXEMPT refactor

Change-Id: I081cb36cfe6cb8098ead6a3d48c43b05dfb210e9