Repository: flutter
Issue: [image_picker] Make ImageSource.gallery open the default gallery app by default
Labels: c: new feature,p: image_picker,package,c: proposal,team-ecosystem,P3,triaged-ecosystem

## Steps to Reproduce

Open the image picker:
var picker = ImagePicker();
var image = await picker.getImage(source: ImageSource.gallery);

**Expected results:** 
a) the gallery app opens
b) if it is possible to select images from different, third party apps like OneDrive, Google Drive, etc., it should work

**Actual results:**
a). The file manager opens and not the gallery App
b). Selecting images from OneDrive (open the drawer, select OneDrive, select an image) does not work => see issue #73099

**Idea**
I expected from the enum ImageSource.gallery that actually the gallery app opens.
To achieve this, we would need to change [launchPickImageFromGallery](https://github.com/flutter/plugins/blob/07dade429d22ca7d8659db2d2fde2fde3acfaae6/packages/image_picker/image_picker/android/src/main/java/io/flutter/plugins/imagepicker/ImagePickerDelegate.java#L334) to use the following Intent instead:

`Intent pickImageIntent = new Intent(Intent.ACTION_PICK, android.provider.MediaStore.Images.Media.EXTERNAL_CONTENT_URI);`

This would ensure the gallery app is opened.

If it is desired for the #pickImage method to also allow selection of images from OneDrive (and others), then it could be changed to:
`   Intent pickImageIntent = new Intent(Intent.ACTION_OPEN_DOCUMENT);
    pickImageIntent.addCategory(Intent.CATEGORY_OPENABLE);
    pickImageIntent.setType("image/*");
`
Then we'd just need some more logic in FileUtils#getPathFromUri: currently the Intents data is always expected to be the file URI. That may not always be the case, it may be necessary to get the uri by invoking:
`val uri = intent.getParcelableExtra<Parcelable>(Intent.EXTRA_STREAM) as Uri`

@cyanglaz: I don't know what's the intended behavior - show the gallery app or the file manager which enables selection from OneDrive and others? I guess it would help to leave the decision which app to open to the caller: ImageSource.gallery could open the gallery app (anything else is not really expected judging from the enum name) and a new enum ImageSource.fileManager could open the file manager. I could provide a pull request with these changes :) 

Flutter doctor output:
alex@S3409:~/Development/xxx/xxx$ fvm flutter doctor -v
[✓] Flutter (Channel stable, 1.22.5, on Linux, locale en_US.UTF-8)
    • Flutter version 1.22.5 at /home/alex/fvm/versions/stable
    • Framework revision 7891006299 (7 weeks ago), 2020-12-10 11:54:40 -0800
    • Engine revision ae90085a84
    • Dart version 2.10.4

[✓] Android toolchain - develop for Android devices (Android SDK version 30.0.2)
    • Android SDK at /home/alex/Android/Sdk
    • Platform android-30, build-tools 30.0.2
    • Java binary at: /opt/android-studio/jre/bin/java
    • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6222593)
    • All Android licenses accepted.

[!] Android Studio
    • Android Studio at /opt/android-studio
    ✗ Flutter plugin not installed; this adds Flutter specific functionality.
    ✗ Dart plugin not installed; this adds Dart specific functionality.
    • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6222593)

[✓] VS Code (version 1.52.1)
    • VS Code at /usr/share/code
    • Flutter extension version 3.19.0

[✓] Connected device (1 available)
    • SM A520F (mobile) • android-arm64 • Android 8.0.0 (API 26)