[PLAT-8680] ordered feature flags

[kstenerud]

Goal

Keep feature flags in the order they were added or modified.

Design

Change the internal representation from a dictionary to an array.

Testing

Updated unit tests to verify ordering.

[github-actions]

Bugsnag.framework binary size decreased by 128 bytes from 815,960 to 815,832 🎉

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +1.2%    +242  +1.2%    +242    [__TEXT]
  [ = ]       0  +4.0%    +128    [__LINKEDIT]
  +0.5%     +40  +0.3%     +40    [__DATA]
  +0.0%     +24  +0.0%     +24    __DATA,__objc_const
  +0.0%     +16  +0.0%     +16    Symbol Table
  -0.4%      -8  -0.4%      -8    Rebase Info
  -0.0%     -10  -0.0%     -10    __TEXT,__objc_methname
  -0.2%     -40  -0.2%     -40    __TEXT,__cstring
  -1.1%     -40  -1.1%     -40    __TEXT,__gcc_except_tab
  -1.8%     -64  -1.8%     -64    __DATA,__const
  -0.1%    -136  -0.1%    -136    String Table
  -0.1%    -152  -0.1%    -152    __TEXT,__text
  -0.0%    -128  [ = ]       0    TOTAL

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