[memory] JavaBuilder.oldState leaks into Workspace.tree

In the heapdump of https://github.com/eclipse-platform/eclipse.platform.releng.aggregator/pull/1612 most memory was hold by org.eclipse.core.internal.resources.Workspace.tree.
VisualVM:

JDKMC:

Workspace.tree is meant to store the state of the Workspace. It does so by storing the history of changes (DeltaDataTree) to the workspace. Interestingly the workspace also stores all IncrementalBuilders which again contain references to the old trees.
I.e the Workspace stores a history of things that contain their history.
That org.eclipse.core.internal.events.InternalBuilder.oldState sounds like a leak - or say - something that unintentionally stores more memory then intended.

I have however no idea how to reduce that since an IncrementalBuilders needs to know the oldState to calculate increments. Just that the old state is stored again as a history feels odd.

リンクされたヒープダンプ解析を出発点として使用し、その後 Workspace.tree、DeltaDataTree、InternalBuilder.oldState を読み、JavaBuilder の oldState 参照も確認してください。builder の状態が保持され続ける理由を追跡し、意図されたライフサイクルを特定してください。レビュー済みのアプローチによって意図しない保持が削減され、インクリメンタルビルドが引き続き正しく動作することを示す証拠が含まれれば、issue は完了です。

索引モデルが issue の本文から書いたものです。