Add examples for Start-DebugAttachSession (#5246)

Adds examples to demonstrate how the new `Start-DebugAttachSession`
function added in PowerShell Editor Services can be used.

Author: jborean93

examples/ChildDebugSessionAttach.ps1

@@ -0,0 +1,22 @@
+# Example on how Start-DebugAttachSession can be used to attach to another
+# process. This launches a child process that runs ChildDebugSessionTarget.ps1
+# but it can be adapted to attach to any other PowerShell process that is
+# either already running or started like this example. To test this example,
+# add a breakpoint to ChildDebugSessionTarget.ps1, select the
+# 'PowerShell Launch Current File' configuration and press F5.
+
+$pipeName = "TestPipe-$(New-Guid)"
+$scriptPath = Join-Path -Path $PSScriptRoot -ChildPath 'ChildDebugSessionTarget.ps1'
+
+$procParams = @{
+    FilePath = 'pwsh'
+    ArgumentList = ('-CustomPipeName {0} -File "{1}" -WaitForAttach' -f $pipeName, $scriptPath)
+    PassThru = $true
+}
+$proc = Start-Process @procParams
+
+Start-DebugAttachSession -CustomPipeName $pipeName -RunspaceId 1
+
+# We need to ensure this debug session stays alive until the process exits. If
+# we exit early then the child debug session will also exit.
+$proc | Wait-Process

examples/ChildDebugSessionTarget.ps1

@@ -0,0 +1,31 @@
+[CmdletBinding()]
+param (
+    [Parameter()]
+    [switch]
+    $WaitForAttach
+)
+
+if ($WaitForAttach) {
+    # For an attach request we need to wait for the debug pipe runspace to be
+    # opened before continuing. There is no builtin way to do this so we
+    # poll the runspace list until a new one is created.
+    $runspaces = Get-Runspace
+    while ($true) {
+        if (Get-Runspace | Where-Object { $_.Id -notin $runspaces.Id }) {
+            break
+        }
+        Start-Sleep -Seconds 1
+    }
+
+    # Windows PowerShell 5.1 will not sync breakpoints until the debugger has
+    # stopped at least once. We use Wait-Debugger to make this happen.
+    if ($PSVersionTable.PSVersion -lt '6.0') {
+        Wait-Debugger
+    }
+    else {
+        Start-Sleep -Seconds 1  # Give the debugger time to sync breakpoints
+    }
+}
+
+$processInfo = "This process is running with PID $PID and has runspace ID $([Runspace]::DefaultRunspace.Id)"
+Write-Host $processInfo  # Place breakpoint here