[PLAT-10016] Use original unhandled value for persisting user-reported events

[yousif-bugsnag]

Goal

Use the original unhandled state of an event and not the overridden unhandled value when determining whether to store an event or upload immediately.

This is more representative of whether the runtime is about to crash, rather than what the developer has changed it to (which is more likely to do with their stability score).

Changeset

• Added a new property originalUnhandledValue to BugsnagHandledState that uses the unhandledOverridden flag to determine the original handled-ness of the event.
• Updated notifyInternal to check originalUnhandledValue when deciding whether to persist an event or send immediately

Testing

• Added a new unit test for originalUnhandledValue
• Manually tested overriding the unhandled flag from a React Native (JS) callback and an onError block

[github-actions]

Bugsnag.framework binary size increased by 176 bytes from 707,136 to 707,312

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.1%     +96  +0.1%     +96    String Table
  +0.0%     +96  +0.0%     +96    __TEXT,__text
  +0.1%     +80  +0.1%     +80    Symbol Table
  +0.1%     +40  +0.1%     +40    __DATA,__objc_const
  +0.1%     +23  +0.1%     +23    __TEXT,__objc_methname
  +0.2%      +8  +0.2%      +8    __DATA,__objc_selrefs
  +0.1%      +4  +0.1%      +4    __TEXT,__unwind_info
  -0.6%     -48  -0.3%     -48    [__DATA]
  -0.5%    -123  -0.5%    -123    [__TEXT]
  [ = ]       0  -1.3%    -176    [__LINKEDIT]
  +0.0%    +176  [ = ]       0    TOTAL

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