Powershell: Comment based help does not work for scripts that start with a shebang

PowerShell does not parse comment based help for a script unless the help comment starts on the first line of the script. This prevents scripts employing a shebang from being helpful via Get-Help.

PowerShell should skip the first line of a script file if it starts with #!.

Steps to reproduce

Create a new script called thing.ps1 with a shebang:

#!/usr/bin/env pwsh
<#
.SYNOPSIS
This does a thing
#>

Expected behavior

PS> Get-Help thing.ps1

NAME
    /Users/aaron/src/thing.ps1

SYNOPSIS
    This does a thing

…

Actual behavior

PS> Get-Help thing.ps1
thing.ps1
…

Environment data

PS> $PSVersionTable

Name                           Value
----                           -----
PSVersion                      6.0.0-beta.9
PSEdition                      Core
GitCommitId                    v6.0.0-beta.9
OS                             Darwin 16.7.0 Darwin Kernel Version 16.7.0: Thu Jun 15 17:36:27 PDT 2017; root:xnu...
Platform                       Unix
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0...}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0