Enable experimental feature to support tab completion on abbreviated cmdlets

[SteveL-MSFT]

PR Summary

While watching some demos at PSConfAsia, it's obvious that cmdlet nouns have gotten descriptive and wordy (Azure and AWS are good examples). This experimental feature enables tab-completion of abbreviated cmdlets and functions:

i-psdf<tab>

returns: Import-PowerShellDataFile

u-akvmssdr<tab>

returns: Undo-AzKeyVaultManagedStorageSasDefinitionRemoval

Note that this only works for tab completion (interactive use), so i-psdf is still an invalid cmdlet name in scripts.

The matching is entirely based on the capital letters of the verb and noun. To test this, create test.json:

{
  "ExperimentalFeatures": [
    "PSUseAbbreviationExpansion"
  ]
}

And run:

pwsh -settingsfile ./test.json

Associated RFC

PR Checklist

• PR has a meaningful title
  • Use the present tense and imperative mood when describing your changes
• Summarized changes
• Change is not breaking
• Make sure all .h, .cpp, .cs, .ps1 and .psm1 files have the correct copyright header
• This PR is ready to merge and is not Work in Progress.
  • If the PR is work in progress, please add the prefix WIP: to the beginning of the title and remove the prefix when the PR is ready.
• User-facing changes
  • Not Applicable
  • OR
  • User-facing Documentation needed
    • Issue filed - Issue link:
• Testing - New and feature
  • Not Applicable or can only be tested interactively
  • OR
  • Make sure you've added a new test if existing tests do not effectively test the code changed
    • Add [feature] if the change is significant or affects feature tests

[anmenaga]

This needs another [feature] test pass to make sure it is green.

[anmenaga]

@daxian-dbw @BrucePay This PR needs your review.

[stale]

This PR has been automatically marked as stale because it has not had activity in the last 30 days. It will be closed if no further activity occurs within 10 days.
Thank you for your contributions.
Community members are welcome to grab these works.

[JamesWTruher]

there's nothing in my comments which are blocking, but I am worried about the case where we have an error (CompletionCompleters, line 193)

[daxian-dbw]

@SteveL-MSFT There is one comment pending #8109 (comment), can you please respond to it?

[daxian-dbw]

LGTM

[iSazonov]

@daxian-dbw Do we add experimental features to Change log? Do we need set CL-* label?