…top sort. reduce mem alloc
# Objective
- Reduce alloc count.
- Improve code quality.
## Solution
- use `TarjanScc::run` directly, which calls a closure with each scc, in closure, we can detect cycles and flatten nodes
follow-up to https://github.com/bevyengine/bevy/pull/7716
# Objective
System access is only populated in `System::initialize`, so without calling `initialize` it's actually impossible to see most ambiguities.
## Solution
- make `initialize` public. The method is idempotent, so calling it multiple times doesn't hurt
# Objective
Fix#7440. Fix#7441.
## Solution
* Remove builder functions on `ScheduleBuildSettings` in favor of public fields, move docs to the fields.
* Add `use_shortnames` and use it in `get_node_name` to feed it through `bevy_utils::get_short_name`.
# Objective
Web builds do not support running on multiple threads right now. Defaulting to the multi-threaded executor has significant overhead without any benefit.
## Solution
Default to the single threaded executor on wasm32 builds.
# Objective
- other tools (bevy_mod_debugdump) would like to have access to the ambiguities so that they can do their own reporting/visualization
## Solution
- store `conflicting_systems` in `ScheduleGraph` after calling `build_schedule`
The solution isn't very pretty and as pointed out it https://github.com/bevyengine/bevy/pull/7522, there may be a better way of exposing this, but this is the quick and dirty way if we want to have this functionality exposed in 0.10.
# Objective
- it would be nice to be able to associate a `NodeId` of a system type set to the `NodeId` of the actual system (used in bevy_mod_debugdump)
## Solution
- make `system_type` return the type id of the system
- that way you can check if a `dyn SystemSet` is the system type set of a `dyn System`
- I don't know if this information is already present somewhere else in the scheduler or if there is a better way to expose it
# Objective
Fixes#7702.
## Solution
- Added an test that ensures that no error is returned if a system or set is inside two different sets that share the same base set.
- Added an check to only return an error if the two base sets are not equal.
# Objective
The `ScheduleGraph` should be expose so that crates like [bevy_mod_debugdump](https://github.com/jakobhellermann/bevy_mod_debugdump/blob/stageless/docs/README.md) can access useful information.
## Solution
- expose `ScheduleGraph`, `NodeId`, `BaseSetMembership`, `Dag`
- add accessor functions for sets and systems
## Changelog
- expose `ScheduleGraph` for use in third party tools
This does expose our use of `petgraph` as a graph library, so we can only change that as a breaking change.
* Add mutated tracker on resources and ChangedRes query for added or mutated resources.
* ResMut:::new() now takes a reference to a 'mutated' flag in its archetype.
* Change FetchResource so that get() returns an Option. Systems using Resources will only be called if all fetched Resources are Some(). This is done to implement ChangedRes, which is Some iff the Resource has been changed.
* Add OrRes for a logical or in tuples of Resource queries.
* Separate resource query get() in is_some() and get() methods for clarity
* Remove unneeded unsafe
* Change ResMut::new()
