(#40) Handle long file paths when caching files

[gep13]

Description Of Changes

This commit adds a new helper method, GetHashedCacheFileName. which is
used to calculate the hashed file name, in a single location, rather
than duplicating the work in multiple places.

Motivation and Context

During testing, it was found that there are cases where a very long
query string was causing a problem when caching the file earlier in the
callstack than the earlier testing. This problem is caused when a call
into a BCL method throws a long file path exception, even though the
Operating System has been enabled to use long path file support. Due
to this, we have introduced a check to see if the file path is longer
than the allowed length, and if it is, immediately create the hashed
filename.

Testing

1. Check out this PR
2. Ensure you have the most recent chocolatey/choco code on your machine
3. Run the update-nuget-client script in the chocolatey/choco repository
4. Clear out the ChocolateyHttpCache folder
5. Open fiddler, and have it running throughout the testing
6. Run the following command choco search --source chocolatey.licensed (use the full URL if required)
7. In fiddler, witness that there are three outgoing queries performed, and that two new files are added to the ChocolateyHttpCache folder. One of these will use a hashed file name, rather than the URI of the query
8. Run choco search --source chocolatey.licensed again
9. Verify that in Fiddler there is only one outgoing query this time
10. Verify that the same list of packages is returned as the initial execution

Operating Systems Testing

Win10

Change Types Made

• Bug fix (non-breaking change).
• Feature / Enhancement (non-breaking change).
• Breaking change (fix or feature that could cause existing functionality to change).
• Documentation changes.
• PowerShell code changes.

Change Checklist

• Requires a change to the documentation.
• Documentation has been updated.
• Tests to cover my changes, have been added.
• All new and existing tests passed?
• PowerShell code changes: PowerShell v2 compatibility checked?

Related Issue

• Fixes Handle potential for long file paths when creating cache files #40

[AdmiringWorm]

LGTM