Add test case for the recording head version feature noted in microso…

…ft#1259 (comment)

azure-pipelines/e2e-ports/overlays/set-detected-head-version/portfile.cmake

@@ -0,0 +1,4 @@
+set(VCPKG_POLICY_EMPTY_PACKAGE enabled)
+if (VCPKG_USE_HEAD_VERSION)
+	set(VCPKG_HEAD_VERSION "detected-head")
+endif()

azure-pipelines/e2e-ports/overlays/set-detected-head-version/vcpkg.json

@@ -0,0 +1,4 @@
+{
+  "name": "set-detected-head-version",
+  "version": "1.0.0"
+}

azure-pipelines/end-to-end-tests-dir/classic-versions.ps1

@@ -1,9 +1,28 @@
 . $PSScriptRoot/../end-to-end-tests-prelude.ps1
 
 # Not a number
+Refresh-TestRoot
 $out = Run-VcpkgAndCaptureOutput @commonArgs install classic-versions-b
 Throw-IfNotFailed
 if ($out -notmatch ".*warning:.*dependency classic-versions-a.*at least version 2.*is currently 1.*")
 {
     throw "Expected to fail and print warning about mismatched versions"
 }
+
+Refresh-TestRoot
+Run-Vcpkg @commonArgs install set-detected-head-version
+Throw-IfFailed
+$listResults = Run-VcpkgAndCaptureOutput @commonArgs list
+if (-Not ($listResults.Trim() -match "set-detected-head-version:[\S]+[\s]+1.0.0"))
+{
+    throw "Expected list to list the declared version"
+}
+
+Refresh-TestRoot
+Run-Vcpkg @commonArgs install set-detected-head-version --head
+Throw-IfFailed
+$listResults = Run-VcpkgAndCaptureOutput @commonArgs list
+if (-Not ($listResults.Trim() -match "set-detected-head-version:[\S]+[\s]+detected-head"))
+{
+    throw "Expected list to list the declared version"
+}