* Remove AHashExt
There is little benefit of Hash*::new() over Hash*::default(), but it
does require more code that needs to be duplicated for every Hash* in
bevy_utils. It may also slightly increase compile times.
* Add StableHash* to bevy_utils
* Use StableHashMap instead of HashMap + BTreeSet for diagnostics
This is a significant reduction in the release mode compile times of
bevy_diagnostics
```
Benchmark #1: touch crates/bevy_diagnostic/src/lib.rs && cargo build --release -p bevy_diagnostic -j1
Time (mean ± σ): 3.645 s ± 0.009 s [User: 3.551 s, System: 0.094 s]
Range (min … max): 3.632 s … 3.658 s 20 runs
```
```
Benchmark #1: touch crates/bevy_diagnostic/src/lib.rs && cargo build --release -p bevy_diagnostic -j1
Time (mean ± σ): 2.938 s ± 0.012 s [User: 2.850 s, System: 0.090 s]
Range (min … max): 2.919 s … 2.969 s 20 runs
```
Relying on TypeId being some hash internally isn't future-proof because there is no guarantee about internal layout or structure of TypeId. I benchmarked TypeId noop hasher vs fxhash and found that there is very little difference.
Also fxhash is likely to be better supported because it is widely used in rustc itself.
[Benchmarks of hashers](https://github.com/bevyengine/bevy/issues/1097)
[Engine wide benchmarks](https://github.com/bevyengine/bevy/pull/1119#issuecomment-751361215)
Previously, if the actual value of LeftStickX was e.g. 0.034 and fluctuated a little
bit (less than the threshold) it would repeatedly send out events,
because it compared the value to the *filtered* old one - 0.0 - which is
more then `0.01` (the threshold) away.
The is fixed by first doing the deadzone and then comparing to the old
value.
Another possible solution would be to store both the actual old value
and the filtered one, but that would add complexity.
improve quality of text2d rendering
* remove coordinate tweaking in sprite-sheet shader
* fixes glyph shimmering of animated text
* reposition glyph before passing it to ab_glyph to normalize its rendering
The result of layout of sequence of glyphs causes individuals to have fractional positions, but since glyph renderings are reused for future instances of that glyph, this produces errors. This change accepts the errors but repositions the glyph to "0, 0" in an effort to get the cleanest possible rendering.
