Declare package visibility needs.

[guilhermeagostinelli]

According to Google:

As you create your app, it's important to consider the set of other installed apps on the device that your app intends to access. If your app targets Android 11 (API level 30) or higher, the system makes some apps visible to your app automatically, but it filters out other apps by default.

If your app targets Android 11 or higher and needs to interact with apps other than the ones that are visible automatically, add the <queries> element in your app's manifest file.

This PR addresses this issue by specifying which packages to query in the AndroidManifest file, so the checkInstalledAppsForShare function can work properly.

Fixes https://github.com/ShekarMudaliyar/social_share/issues/81

[guilhermeagostinelli]

p.s. another option would be to specify in the README the need of adding the <queries> element to the app's AndroidManifest.xml, thus transferring the responsibility of this step to the user. This would allow the user to specifically choose which packages he would like to add under the <queries> tag.