fix: stay in call screen after back button from fullscreen [WPB-640]

[Garzas]

WPB-640 When video is maximized and user taps on back button, video should minimise

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• The PR Title

  • conforms to the style of semantic commits messages¹ supported in Wire's Github Workflow²
  • contains a reference JIRA issue number like SQPIT-764
  • answers the question: If merged, this PR will: ... ³

• The PR Description

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What's new in this PR?

Issues

When user clicks back button on full screen video in call then it closes entire call screen instead stay in it.

Solutions

Add BackHandler in full screen tile to get back to call screen

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 43.53%. Comparing base (2ff2e04) to head (64ada69).

Additional details and impacted files

@@             Coverage Diff              @@
##           develop    #2795       +/-   ##
============================================
+ Coverage         0   43.53%   +43.53%     
============================================
  Files            0      413      +413     
  Lines            0    13903    +13903     
  Branches         0     2516     +2516     
============================================
+ Hits             0     6052     +6052     
- Misses           0     7139     +7139     
- Partials         0      712      +712     

Files	Coverage Δ
...id/ui/calling/ongoing/fullscreen/FullScreenTile.kt	0.00% <ø> (ø)

... and 412 files with indirect coverage changes

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[github-actions]

Test Results

860 tests  ±0   860 ✅ ±0   7m 36s ⏱️ - 4m 51s
117 suites ±0     0 💤 ±0 
117 files   ±0     0 ❌ ±0 

Results for commit 64ada69. ± Comparison against base commit 2ff2e04.

[github-actions]

APKs built during tests are available here. Scroll down to Artifacts!

[AndroidBob]

Build 3638 succeeded.

The build produced the following APK's:

• com.wire.android-v4.7.0(9171599)(9171599)-staging-compat.apk