Per the request of spaceman_atlas, the No Release mod is rewritten to
avoid modifications to DrawableHoldNoteTail. The approach is based
on that of the Strict Tracking mod for the osu!(standard) ruleset,
injecting the mod behavior by replacing the normal hold note with
the mod's variant. The variant inherits most bevaior from the normal
hold note, but when creating nested hitobjects, it creates its own
hold note tail variant instead, which in turn is used to instantiate
the mod's variant of DrawableHoldNoteTail with a new behavior.
The time a judgement is awarded is changed from the end of its
Perfect window to the time of the tail itself.
The new test scene is essentially a copy of TestSceneHoldNoteInput,
modified to test the judgement changes applied by the new mod. A base
class might need to be abstracted out for them.
This was reported in https://github.com/ppy/osu/pull/28474, albeit the
code changes proposed there did not fix the issue at all.
See 8b6385f7d0 for demonstration of the
crash scenario. Basically what is happening there is:
- The starting premise is that there is a spinner placement active.
- At this time, a drag selection is started via the timeline.
- Once the drag selection finds at least one suitable object to select,
it mutates `SelectedItems`.
- When selection changes for any reason, the `HitObjectComposer`
decides to switch to the "select" tool, regardless of why
the selection changed.
- Changing the active tool causes the current placement - if any -
to be committed, which mutates the beatmap.
- Back at the drag box selection code, this causes a "collection
modified when enumerating" exception.
The proposed fix here is to eagerly commit active placement - if any -
when drag selection is initiated via the timeline, which avoids this
issue. This also appears to vaguely match stable behaviour and is sort
of consistent with the logic of committing any outstanding changes upon
switching to the selection tool.
