bsn: fix accidental scene entity deduplication due to name references

[laundmo]

Objective

The changes introduced in

• bsn: Allow passing EntityTemplate into scene functions and Scene Component @props #24174

only used the exact macro invocation file/line/column plus a per-macro name id from a counter as the key for SceneEntityReference.

That means if the same bsn macro with a fixed entity name is called multiple times it will only spawn a single entity instead of however often it was called. This is clearly buggy behaviour.

Solution

This PR introduces a runtime call-counter which is only added if named entity references are used, and is incremented with each call to the macro. This is then used as part of the key, making sure entities from different calls to the generated code are treated as distinct.

It also vastly improves the handling of #{expr} names, which were previously incompletely handled.

Testing

• cargo test in bevy_scene with new test for this issue
• Test with the code of the original reporter, @chyrr. on discord and perhaps @ashikun who ran into this as well
• Run examples
• Benchmark (uh oh, i'm a bit afraid of those...)

[laundmo]

CI failures: i can fix the typo, but the other one is a failure in bevy_reflect which this PR doesn't touch