Fix Rate menu item availability in help/support dialogs

[lukstbit]

This PR fixes some bugs related to code around the Rate menu item from the help/support dialogs. Changes:

• removes the code related to Rate from HelpDialog.createInstance() because the option is not used at all in the help menu. This also allows the simplification of the method by removing its context parameter.
• fixes a bug related to Rate from HelpDialog.createInstanceForSupportAnkiDroid() which made the Rate menu option to appear even if the application to handle it is not present on the device. See the before and after picture below on a device which doesn't have the play store app installed:

On the majority of devices with the store application available there are no changes and the Rate menu option is available:

• fixes the testMenuSupportAnkiDroidShowsRateWhenPossible() test which was passing be luck. Although the menu has 6 items(see above the bug) the test passed because it looked for 5 children in the dialog and Robolectric allows only a set height for the RecyclerView(which resulted in the view to have 5 children ). The fix was to use the adapter which is a source of truth not affected by UI issues.
• added a test to make sure the dialog shows the Rate menu item when the store app is available(important as the Robolectric environment doesn't have it)
• some cleanups for the tests, is to equalTo, as I already touched those lines

How Has This Been Tested?

Ran the tests, manually checked the dialogs.

Checklist

• [x] You have not changed whitespace unnecessarily (it makes diffs hard to read)
• [x] You have a descriptive commit message with a short title (first line, max 50 chars).
• [x] Your code follows the style of the project (e.g. never omit braces in if statements)
• [x] You have commented your code, particularly in hard-to-understand areas
• [x] You have performed a self-review of your own code
• [x] UI changes: include screenshots of all affected screens (in particular showing any new or changed strings)
• [ ] UI Changes: You have tested your change using the Google Accessibility Scanner