[INSD-9704] Fix The onInvoke Callback

[a7medev]

Description of the change

The BugReporting.setOnInvokeCallback API breaks the Instabug.show API because the on-invoke doesn't get called on the main thread which causes the native Android SDK to produce the following error:

E/IBG-Core(22608): Instabug failed to execute {Instabug.show} due toMethods marked with @UiThread must be executed on the main thread. Current thread: IBG-API-executor-0

This PR fixes this issue by running the on-invoke callback for Flutter on the main thread.

Type of change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Related issues

Issue links go here

Checklists

Development

• Lint rules pass locally
• The code changed/added as part of this pull request has been covered with tests

Code review

• This pull request has a descriptive title and information useful to a reviewer
• Issue from task tracker has a link to this pull request

[InstabugCI]

Coverage Report

Label	Coverage	Status
Dart	83.7%	✅

Generated by 🚫 dangerJS against b24aa00

[asamiz]

This is an approval from me, good job as always @a7medev.