Add 3 starting point pixel art

[ClementPasteau]

No description provided.

[github-actions]

Preview the game(s) changed or added in this Pull Request

• https://editor.gdevelop.io?project=https://raw.githubusercontent.com/GDevelopApp/GDevelop-examples/add-pixel-art-starting-points/examples/starting-physics-pixel/starting-physics-pixel.json
• https://editor.gdevelop.io?project=https://raw.githubusercontent.com/GDevelopApp/GDevelop-examples/add-pixel-art-starting-points/examples/starting-physics/starting-physics.json
• https://editor.gdevelop.io?project=https://raw.githubusercontent.com/GDevelopApp/GDevelop-examples/add-pixel-art-starting-points/examples/starting-platformer-pixel/starting-platformer-pixel.json
• https://editor.gdevelop.io?project=https://raw.githubusercontent.com/GDevelopApp/GDevelop-examples/add-pixel-art-starting-points/examples/starting-top-down-pixel/starting-top-down-pixel.json

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This is an automatic message displaying links to the games in this PR - double check the JSON in case of doubt.

[github-actions]

Images automagically compressed by Calibre's image-actions ✨

Compression reduced images by 13%, saving 5.81 KB.

Filename	Before	After	Improvement	Visual comparison
examples/starting-physics-pixel/assets/PixelBackground.png	200 bytes	171 bytes	-14.5%	View diff
examples/starting-physics-pixel/assets/StartingPixelBall.png	339 bytes	253 bytes	-25.4%	View diff
examples/starting-physics-pixel/assets/StartingPixelBlock.png	165 bytes	138 bytes	-16.4%	View diff
examples/starting-physics-pixel/assets/StartingPixelGround.png	203 bytes	167 bytes	-17.7%	View diff
examples/starting-physics-pixel/assets/StartingPixelWall.png	148 bytes	142 bytes	-4.1%	View diff
examples/starting-physics-pixel/preview.png	30.10 KB	25.24 KB	-16.2%	View diff
examples/starting-platformer-pixel/assets/PixelBackground.png	200 bytes	171 bytes	-14.5%	View diff
examples/starting-platformer-pixel/assets/StartingPixelCoin.png	116 bytes	106 bytes	-8.6%	View diff
examples/starting-platformer-pixel/assets/StartingPixelGround.png	203 bytes	167 bytes	-17.7%	View diff
examples/starting-platformer-pixel/assets/StartingPixelPlayer.png	227 bytes	189 bytes	-16.7%	View diff
examples/starting-platformer-pixel/preview.png	11.10 KB	10.90 KB	-1.9%	View diff
examples/starting-top-down-pixel/assets/StartingPixelGroundTilemap.png	1.04 KB	780 bytes	-26.8%	View diff
examples/starting-top-down-pixel/assets/StartingPixelObstacle.png	265 bytes	180 bytes	-32.1%	View diff
examples/starting-top-down-pixel/assets/StartingPixelPlayer.png	286 bytes	202 bytes	-29.4%	View diff
examples/starting-top-down-pixel/assets/StartingPixelWall.png	144 bytes	140 bytes	-2.8%	View diff

6097 images did not require optimisation.