[bean completion proposals] improve performance of additional edits showing up

There is a significant lag between the completion being activated and the additional edits showing up in the editor. This causes a slightly weird and irritating moment, since additional text edits happen in the editor at a moment that is somewhat disconnected from the user interaction (of selecting the proposal). This lag also causes difficulties in a fast and fluent editing experience, for example when adding a method invocation to the bean variable that got introduced by the completion.

Start at the bean completion proposals entry point and investigate the timing between proposal activation and additional edits appearing in the editor. Reproduce the lag while adding a method invocation to the introduced bean variable; done means the additional edits appear without a noticeable delay or disconnect from the selection.