SWEEP: Avoid unnecessary FileInfo/DirectoryInfo allocations, #832

[paulirwin]

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Add string-based overloads to some methods that take FileInfo/DirectoryInfo to avoid unnecessary allocations

Fixes #832

Description

See #832 for context. This makes changes to add and prefer string-based overloads for methods that take FileInfo and DirectoryInfo primarily just for the FullName property, to avoid unnecessary allocations.