Consider not using Path.GetDirectoryName in ViewStartUtility

[pranavkm]

Today given an app relative path, we use Path.GetDirectoryName to determine potential paths for _ViewStart.cshtml. Path.GetDirectoryName does a bunch of operations to figure out if the path is absolute and sanitizing which shows up in perf profiles. Additionally, it attempts to normalize the directory separator

var path = Path.GetDirectoryName("foo/bar/baz"); // foo\bar

Since these paths are generated from the Razor view engines, an option would be to consider simply substring-ing the passed in path rather than using Path.GetDirectoryName. Some discussion about this is available at #1996 (comment)

[rynowak]

This bug isn't relevant anymore, we've already decided to cache all of this data as part of the changes in #3364. After that PR is checked in, we'll profile and identify any new issues that crop up.

Closing as this is not actionable anymore.

[pranavkm]

We actually fixed this as part of #3294. Closing this as dup