Filter out path separators in package names

[anamnavi]

Utils.ProcessNameWildcards detects and potentially filters out wildcard characters and unwanted characters from Name input. Save-PSResource and other cmdlets call this method. This method will now also filter out path separator characters at the start of a package name, if present, and write an appropriate error message. When a path separator is present at the start some servers (like V3 API ones) ignore or filter it out, and make a successful request for the package but then our own comparisons against the package name later fail, so it is better to filter out path separators at the start and be clearer with the error.

PR Summary

PR Context

Fixes #1901

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[anamnavi]

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[anamnavi]

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