Adds dispose{} named block keyword to language files. Yay, editor highlighting! 🎉

function Get-Foo {
    [CmdletBinding()]
    param()

    begin { }
    process { }
    end { }
    dispose { }
}

Reference PowerShell/PowerShell#9900 for indication on when the feature will become available. From current team decisions it appears it will likely be merged post-v7 and generally available the following release.

This is all the references to named blocks I could find, and I updated an example or two while I was at it. If I missed anything, please let me know.

/cc @TylerLeonhardt