fix image scale quality and update to latest flutter version

[xsm1997]

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This PR fixed the scale quality of photo-view and fixed some dependency problems so that we can update to the latest flutter SDK version.

1. fix image scale quality: the default filterQuality of photo-view is none, whose algorithm is nearest neighbor up-sampling. Compared with the native Image widget of Android, it is more suitable to use medium filter quality (bilinear interpolation), which has a much favorable looking and is also fast for modern devices.

2. update dependencies: updated flutter_slidable and extended_text to fix compile errors. Updated rounded_loading_button to a custom fork, as the main repo has not update for a long time. We can use version 3.19.2 for now.