CATROID-1622 Improve script block scrolling

[Frajhamster]

https://catrobat.atlassian.net/browse/CATROID-1622

• Script block scrolling now works as user would expect (No more weird jittering around)
• Once user reaches top/bottom edge of the screen, the scrolling begins
• Scrolling ends, once user goes away from the edges

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[reichli]

Looks good, thank you!