Add PSReadLine module files

These are copied from `src/Microsoft.PowerShell.PSReadLine`, which is
necessary until .NET CLI has better support for specifying
source/destination content information (which is coming soon).

src/Modules/PSReadLine/PSReadLine.psd1

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+@{
+RootModule = 'PSReadLine.psm1'
+NestedModules = @("Microsoft.PowerShell.PSReadLine.dll")
+ModuleVersion = '1.2'
+GUID = '5714753b-2afd-4492-a5fd-01d9e2cff8b5'
+Author = 'Microsoft Corporation'
+CompanyName = 'Microsoft Corporation'
+Copyright = '(c) Microsoft Corporation. All rights reserved.'
+Description = 'Great command line editing in the PowerShell console host'
+PowerShellVersion = '3.0'
+DotNetFrameworkVersion = '4.0'
+CLRVersion = '4.0'
+FunctionsToExport = 'PSConsoleHostReadline'
+CmdletsToExport = 'Get-PSReadlineKeyHandler','Set-PSReadlineKeyHandler','Remove-PSReadlineKeyHandler',
+                  'Get-PSReadlineOption','Set-PSReadlineOption'
+HelpInfoURI = 'http://go.microsoft.com/fwlink/?LinkId=528806'
+}

src/Modules/PSReadLine/PSReadLine.psm1

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+function PSConsoleHostReadline
+{
+    Microsoft.PowerShell.Core\Set-StrictMode -Off
+    [Microsoft.PowerShell.PSConsoleReadLine]::ReadLine($host.Runspace, $ExecutionContext)
+}