[Wi-Fi] Use getUriHelpString() result to judge if Settings APP should register...

[Wi-Fi] Use getUriHelpString() result to judge if Settings APP should register the help button click event and file related intent if need.

The Openroaming help button should show only when the getHelpUriString() value is not null, and need to handle the click event in Settings APP.

Bug: 146669261
Test: Adjust unit test cases:
      1. make RunSettingsRoboTests ROBOTEST_FILTER=WifiEntryPreferenceTest
      2. make RunSettingsRoboTests ROBOTEST_FILTER=WifiSettings2Test
Change-Id: I27a717c3014b01cc464908bac56f64bd08aa5da3