[share_plus] minSdkVersion 16 & graceful fallback

[Coronon]

Description

• Revert minSdkVersion back to 16 and dynamically determine support for shareWithResult at runtime
• Gracefully fall back to "normal" share without result if the environment does not support shareWithResult
• Improve documentation for shareWithResult

Related Issues

Closes #789

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[Coronon]

The conflicts are due to #797. I will resolve them tonight (mainly formatting).

Update: rebased

[miquelbeltran]

Thanks! The original share method, could it be replaced by the one with the result? There's no difference except for the return type, which was void in the original share method, and now it would be ShareResult.

[Coronon]

Did not think about that - yeah, that would definitely simplify the API. The only problem I see is people not awaiting the "old" share methods and then complaining about the "not awaited..." error because lets face it: most people just update and don't read the changelog ^^

[vbuberen]

Left a few comments on namings.

What we are currently missing is updates to docs, which appear on Plus plugins website.
Would be good if you also modify https://github.com/fluttercommunity/plus_plugins/blob/main/docs/share_plus/usage.mdx to mention new methods and description about fallback on unsupported platforms.

[Coronon]

Also added shareWithResult and shareFilesWithResult to the usage.mdx docs.

Will commit & push when isWithResultAvailable naming is resolved.

EDIT: pushed

[Mosc]

Thanks! The original share method, could it be replaced by the one with the result? There's no difference except for the return type, which was void in the original share method, and now it would be ShareResult.

@Coronon already touched on it a bit, but there's a difference in behavior between share and this updated shareWithResult (at least on Android SDK >= 22, iOS and macOS). awaiting the former completes immediately while the latter completes only after the share dialog is dismissed. Replacing share's implementation could cause issues in existing code. I'm not necessarily against such a change, but as I tried to argue on #797, any breaking change should be made with caution and should be accompanied by an appropriate increase in version number. The current PR is itself already a nice improvement, so I suggest we try to merge this iteration first.

[vbuberen]

LGTM. Thanks for this contribution!
Would like to wait for a review from Miguel as he was the person, who started reviewing this PR.

[miquelbeltran]

LGTM too, I will go ahead and merge & release

[uc-asa]

I'm still getting this issue and android always return null in raw