Check for changes when user reopens data set or member

[adam-wolfe]

Is your feature request related to a problem? Please describe.

If I open a member with Zowe Explorer, then close it, when I reopen that member later in the same VS Code session, I may be working with a cached version of the member that does not match what is currently on the mainframe.

Describe the solution you'd like

Zowe Explorer should check for changes on the mainframe and download the latest contents when the user opens a data set or member in a tab.

If there are concerns about automatically downloading the latest version when reopening something, we could consider adding a prompt to tell the user that the file has changed on the mainframe, and then give the user the option to get the latest version or keep their cached version.

Describe alternatives you've considered

Use Pull from Mainframe, though I think it's fair to assume that if a user closes an editor tab for a member (which will require them to either save or discard any changes they may have made), and eventually reopens that member, a user will want to see contents that match what is on the mainframe.

Additional context

This may also be a valid suggestion for the USS and Jobs trees.

[JWaters02]

This (and #4346 ) are not enhancements, they are bugs, as I'm pretty sure this functionality should already exist - in that when a file updates on mainframe, the data set should automatically be refreshed either when open in editor or when re-opened, without having to pull from mainframe (unless they have unsaved changes). I definately remember seeing issue(s) relating to these bugs in the last few months but I couldn't find any.