## Objective
- Add an arrow gizmo as suggested by #9400
## Solution
(excuse my Protomen music)
https://github.com/bevyengine/bevy/assets/14184826/192adf24-079f-4a4b-a17b-091e892974ec
Wasn't horribly hard when i remembered i can change coordinate systems
whenever I want. Gave them four tips (as suggested by @alice-i-cecile in
discord) instead of trying to decide what direction the tips should
point.
Made the tip length default to 1/10 of the arrow's length, which looked
good enough to me. Hard-coded the angle from the body to the tips to 45
degrees.
## Still TODO
- [x] actual doc comments
- [x] doctests
- [x] `ArrowBuilder.with_tip_length()`
---
## Changelog
- Added `gizmos.arrow()` and `gizmos.arrow_2d()`
- Added arrows to `2d_gizmos` and `3d_gizmos` examples
## Migration Guide
N/A
---------
Co-authored-by: Nicola Papale <nicopap@users.noreply.github.com>
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