Improve type inference for $_

[MartinGC94]

PR Summary

Fixes the type inference for $_ in pipelines with more than 1 command by making it infer the type of the previous command of the expression rather than the first.

-Edit: Decided to make a full fix for $_ and also fix it when the scriptblock is inside an array of arguments like for Select-Object or Foreach-Object ls | ForEach-Object -Process {$_.<Tab>},{$_.<Tab>}
Also fixes a scenario where a catch block is given invalid types so there's no completion for $_ inside the catch block.
Fixes: #17613
Edit2: The test failures helped me discover a different issue, strings are enumerated as chars by the type inference. This has now been fixed.

Full list of scenarios where $_ is now properly being inferred:

• Member invocation scriptblocks like $Collection.Where({$_})
• Scriptblocks used as command arguments like: ls | where {$_}
• Switch statements like: switch ("hello") {'Hello'{$_}}
• Catch statements like: try{} catch {$_}
• Trap statements like: trap {$_}

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[daxian-dbw]

Looks good, but it would be great if more comments can be added.

[MartinGC94]

Sorry for pushing new updates after the review, I forgot that there were other instances where $_ is set. Hopefully I have them all now.

[daxian-dbw]

Looks great! Thank you, @MartinGC94!

[ghost]

🎉v7.3.0-preview.7 has been released which incorporates this pull request.:tada:

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