* Adding PowerShellHelpFiles package which contains default.help.txt to powershell-win-core
* Adding test case to validate that <pshome>/<culture>/default.help.txt is present. This is done by calling 'Get-Help'
* Updating get-help to skip searching for the help file when the InternalTestHooks.BypassOnlineHelpRetrieval is enable. This way, we force get-help to generate a metadata driven help object, which includes a helpUri that points to the fwlink defined in the cmdlet code.
* Updating get-help -online <cmdletName> tests to not delete the help files. Instead, I've added logic to get-help to not find the help file when the test hook BypassOnlineHelpRetrieval is enable.