fix double tapping in gallery

[clragon]

This MR attempts to fix #216

Using the Code provided by @deckerst migrated to null safety.

I have adjusted the touch slope factor for panning and it seems to work decently.

[ZahraVe]

I still have tapping issue on samsung phons (android 10). Could you please help me to fix the issue?
I am using ;
photo_view: ^0.12.0
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[✓] Flutter (Channel stable, 2.2.3, on macOS 11.2.3 20D91 darwin-arm, locale en-GB)
[✓] Android toolchain - develop for Android devices (Android SDK version 30.0.3)
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[✓] Android Studio (version 4.1)
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[clragon]

@ZahraVe I cannot help you fix this,
this PR has it's own issues.

@renancaraujo said there might be a rewrite in the future
and that might fix double tapping.

For now there is no solution to this.

[ZahraVe]

@clragon Thanks for your response.

I have directly messaged @renancaraujo as he said 'if someone finds an issue in this matter after updating to 0.10.3, feel free to retake the discussion or message me on discord and I will attack this asap.' in #293 (comment) . Still waiting for any answer if they really work on this issue and if there is any hope to see it is fixed in near future.

Is there any alternative way of implementing or any other plugin that I can use instead ?

[clragon]

@ZahraVe you seem to have not understood my message.

There is currently no fix for the double tap issue.
It is not fixed in any released version.

issue #293 is not related to the double tap issue.
the issue you are looking for is #216.

[ZahraVe]

@clragon Seems I am a bit confiused among all gesture issues related to this plugin. But I got your point. Thanks anyway. so I need to have a look at other options. What is the alternative for this plugin in your opinion? thanks for youe help.