[url_launcher] Improved documentation of the `headers` parameter. (fl…

…utter#3097)

Added a clear documentation of the fact that the headers parameter at the launch method is not fully supported by all external browsers.

[google_maps_flutter_web] Fix InfoWindow snippets. (flutter#3156)

[google_sign_in] fix merge error in CHANGELOG (flutter#3153)

[google_sign_in] fix merge error in CHANGELOG (flutter#3153)

[google_sign_in] fix merge error in CHANGELOG (flutter#3153)

[google_sign_in] fix merge error in CHANGELOG (flutter#3153)

[share] Replace deprecated Environment.getExternalStorageDirectory() …

…call on Android. (flutter#3152)

* Android API 29 & 30

* Update Version

[google_sign_in] fix merge error in CHANGELOG (flutter#3153)

[google_sign_in] fix merge error in CHANGELOG (flutter#3153)

[google_sign_in] fix merge error in CHANGELOG (flutter#3153)