Improve type inference of hashtable keys

[MartinGC94]

PR Summary

Updates the hashtable visitor so all members are inferred and not just "pure" expressions.
Also updates type inference for the IndexExpression to support synthetic types.

This enables tab completion scenarios like: $Hashtable=@{Key1=ls};$Hashtable.Key1.<Tab> to properly infer the type from the command.

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[ghost]

This pull request has been automatically marked as Review Needed because it has been there has not been any activity for 7 days.
Maintainer, please provide feedback and/or mark it as Waiting on Author

[iSazonov]

If PSTypeName("System.Object") is immutable makes sense allocate this again and again?

[MartinGC94]

How would you avoid that? Use a field?

[iSazonov]

First question - is it a hot path or no? If yes we could use a field with lazy initialization.

[MartinGC94]

Hard to say. It's just a fallback for when PowerShell can't infer the type in the value expression, or when the user uses a literal $null as the value so in theory it should rarely be used. The only realistic scenario where I think it would be hot is if the user is analyzing a hashtable that uses a bunch of commands/types that are unavailable because the module hasn't been installed on the computer. In that case it would be run for each key/value pair in the hashtable.

[iSazonov]

LGTM with one minor comment.

[daxian-dbw]

LGTM

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This PR has 46 quantified lines of changes. In general, a change size of upto 200 lines is ideal for the best PR experience!

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Size       : +31 -15
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Total files changed: 2

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.cs : +23 -15
.ps1 : +8 -0

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