CmdPal: entirely redo the Run page

[zadjii-msft]

Just filing so I can track my remaining todo's

This entirely rewrites the shell page. It feels a lot more like the old run dialog now.

• It's got icons for files & exes
• it can handle network paths
• it can handle commands /with args...
• it'll suggest files in that path as you type
• it handles %environmentVariables%
• it handles "Paths with\spaces in them"
• it shows you the path as a suggestion, in the text box, as you move the selection

References:
#39044
#39419
#38298

Remaining todo's

• Remove the GenerateAppxManifest change, and file something to fix that. We are still generating msix's on every build, wtf
• Clean-up code
• Double-check loc
• Remove a bunch of debug printing that we don't need anymore
• File a separate PR for moving the file (indexer) commands into a common project, and re-use those here
• Add history support again! I totally tore that out
• make shell: paths and weird URI's just work. Good test is x-cmdpal://settings

further optimizations that probably aren't blocking

• Our fast up-to-date is clearly broken, but I think that's been broken since early 0.91
• If the exe doesn't change, we don't need to create a new ListItem for it. We can just re-use the current one, and just change the args
• if the directory hasn't changed, but we typed more chars (e.g. c:\windows\s -> c:\windows\sys), we should cache the ListItem's from the first query, and re-use them if possible.