[webview_flutter] Fix pedantic lint errors (flutter#2322)

[video_player] Fix pedantic lints (flutter#2321)

Fix pedantic lints. This fixes some potential race conditions in cases where
futures within some video_player methods weren't being awaited correctly.

[share] Fix pedantic lints (flutter#2320)

[package_info] Fix pedantic lints (flutter#2319)

This involved internally refactoring how the `PackageInfo.fromPlatform`
code handled futures, but shouldn't change existing functionality.

[in_app_purchase] Fix most failing pedantic lints (flutter#2317)

None of these fixes should affect functionality. There are dozens of
undocumented public API members that still need to be documented to
completely remove the analysis_options for this package.

[e2e] Fix pedantic lints (flutter#2315)

[device_info] Fix pedantic errors (flutter#2314)

[connectivity] Fix unawaited futures (flutter#2313)

[battery] Fix pedantic linter errors (flutter#2311)

[android_alarm_manager] Update minimum Flutter version to 1.12.0 (flu…

…tter#2327)