Simplify the layout of the onboarding splash screen

[pixlwave]

Fixes #6319 by simplifying the layout of the splash screen:

• The gradient is now separate from the carousel pages
• The carousel pages are now in a VStack with the buttons rather than using a ZStack and ViewFrameReader.

The second commit in the PR updates the structure of the splash screen to match the other SwiftUI screens with the body above all of the other views. It is probably easiest to review this PR by commit because of this.

Edit: It turns out all of these changes didn't fix the issue, what did was increasing the maxWidth on the carousel images in the last commit. Tested with screens of 320pt, 375pt, 390pt, 414pt and 428pt and no stuttering noticed, but this feels like a rather fragile assumption 😕

iPod Touch	iPhone SE (3rd gen)	iPhone 13 Mini	iPhone 13 Pro Max

11" iPad Portrait	11" iPad Landscape

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

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[codecov-commenter]

Codecov Report

Merging #6320 (80e54b3) into develop (a8514ed) will increase coverage by 0.00%.
The diff coverage is 93.81%.

@@           Coverage Diff            @@
##           develop    #6320   +/-   ##
========================================
  Coverage     6.24%    6.24%           
========================================
  Files         1440     1440           
  Lines       155412   155419    +7     
  Branches     62532    62533    +1     
========================================
+ Hits          9705     9713    +8     
+ Misses      145302   145301    -1     
  Partials       405      405           

Impacted Files	Coverage Δ
.../Modules/Onboarding/Common/OnboardingMetrics.swift	100.00% <ø> (+100.00%)	⬆️
...ing/SplashScreen/View/OnboardingSplashScreen.swift	58.66% <91.52%> (+1.92%)	⬆️
...SplashScreen/View/OnboardingSplashScreenPage.swift	81.25% <95.45%> (-3.20%)	⬇️
...ng/SplashScreen/OnboardingSplashScreenModels.swift	90.00% <100.00%> (+2.50%)	⬆️
...dules/Common/ViewFrameReader/ViewFrameReader.swift	0.00% <0.00%> (-100.00%)	⬇️
...ojiPicker/Data/EmojiMart/EmojiItem+EmojiMart.swift	95.65% <0.00%> (+0.30%)	⬆️
...UI/Modules/Common/Util/ReadableFrameModifier.swift	100.00% <0.00%> (+100.00%)	⬆️

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[github-actions]

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[aringenbach]

LGTM 👍

I'm not sure we can have a better fix anyway (I was thinking about nesting the Image in a container and applying some of the frame modifiers to the container and see what happens, but I'm not sure how much effort we want to put into something that looks like a pure iOS/SwiftUI issue).

[pixlwave]

Note: There's a second review on these changes on ElementX.