iOS: move HeadlessPlayerImpl from PlayerUIInternalTestUtilities to PlayerUITestUtilitiesCore

[nancywu1]

Move HeadlessPlayerImpl PlayerUITestUtilitiesCore so it can be exposed and used by test helpers in FTR

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• [x] patch
• [ ] minor
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  📦 Published PR as canary version: 0.8.1--canary.500.17272

  
  Try this version out locally by upgrading relevant packages to 0.8.1--canary.500.17272

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 91.91%. Comparing base (ae9a118) to head (a7bbe93). Report is 42 commits behind head on main.

Files with missing lines	Patch %	Lines
...ls-core/Sources/utilities/HeadlessPlayerImpl.swift	80.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #500 +/- ## ========================================== - Coverage 91.97% 91.91% -0.06% ========================================== Files 340 341 +1 Lines 26960 27002 +42 Branches 1945 1945 ========================================== + Hits 24796 24820 +24 - Misses 2150 2168 +18 Partials 14 14 ```

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[nancywu1]

/canary

[nancywu1]

/canary