Modify PollingWildCardChangeToken to include the timestamp of the files along with the names as part of hash check

[pranavkm]

Consider the following timeline

t0 ->  Create a copy of  File.txt to a backup directory . 
t1 -> Modify File.txt with contents different from the original file.
t2 -> Move the file from the backup directory to the original location.

The PollingWildCardChangeToken only carries the timestamp of the most recently changed last write time window. Consequently this wouldn't work when a file is modified but it's timestamp hasn't moved forward. We could avoid this by additionally storing the timestamp along with the name of the file.

[pranavkm]

cc @Eilon

[Eilon]

Not a task. This is a genuine bug. Tasks are for code cleanup!