Improve hashtable key completion for type constrained variable assignments, nested hashtables and more

[MartinGC94]

PR Summary

Fixes PowerShell/PowerShellEditorServices#1852
Decided to make a full fix for all hashtable key completion scenarios I could think of:

• Fixes type inference for ConvertExpressions that use a PowerShell type that hasn't been loaded yet.
• Fix tab completion for constructor hashtables so it only completes properties if the class has a null constructor or if it's an interface.
• Fix tab completion for constructor hashtables that use a PowerShell type that hasn't been loaded yet.
• Fix tab completion for nested hashtables like: Get-WinEvent -FilterHashtable @{SuppressHashFilter=@{<Tab>
• Fix tab completion for hashtables that are in an array of arguments like: ls | select Name,@{<Tab>}
• Add the same property completion that exists for type conversions to typed variables command parameters and Property assignments
• Add completion for the module specification used in using module @{<Tab>

PR Context

PR Checklist

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• Make sure all .h, .cpp, .cs, .ps1 and .psm1 files have the correct copyright header
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• Breaking changes
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  • Experimental feature(s) needed
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• User-facing changes
  • Not Applicable
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  • Documentation needed
    • Issue filed:
• Testing - New and feature
  • N/A or can only be tested interactively
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  • Make sure you've added a new test if existing tests do not effectively test the code changed
• Tooling
  • I have considered the user experience from a tooling perspective and don't believe tooling will be impacted.
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  • I have considered the user experience from a tooling perspective and opened an issue in the relevant tool repository. This may include:
    • Impact on PowerShell Editor Services which is used in the PowerShell extension for VSCode
      (which runs in a different PS Host).
      • Issue filed:
    • Impact on Completions (both in the console and in editors) - one of PowerShell's most powerful features.
      • Issue filed:
    • Impact on PSScriptAnalyzer (which provides linting & formatting in the editor extensions).
      • Issue filed:
    • Impact on EditorSyntax (which provides syntax highlighting with in VSCode, GitHub, and many other editors).
      • Issue filed:

[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

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This PR has 362 quantified lines of changes. In general, a change size of upto 200 lines is ideal for the best PR experience!

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Label      : Large
Size       : +256 -106
Percentile : 76.2%

Total files changed: 3

Change summary by file extension:
.cs : +191 -77
.ps1 : +65 -29

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[iSazonov]

@SeeminglyScience Please review.

[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

[daxian-dbw]

Sorry for taking so long to review. Not finished yet, but want to share feedback so far.

[daxian-dbw]

I'm fine the use of goto LABEL here to break out of the loop. It's not that confusing to get what it does by reading the code.

[daxian-dbw]

@MartinGC94 Thanks for the contribution and I appreciate your patience.

[andyleejordan]

This is awesome work!

[ghost]

🎉v7.4.0-preview.4 has been released which incorporates this pull request.:tada:

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