wpf: delay-load UIAutomationCore because it's incomplete in RS1 (#15614)

UiaRaiseNotificationEvent is not present on Windows Server 2016, even
though it is documented as being present.
This also removes the cost of loading up UIAutomationCore from the
critical path.

.github/actions/spelling/allow/apis.txt

@@ -29,6 +29,7 @@ Dacl
 dataobject
 dcomp
 DERR
+delayimp
 dlldata
 DNE
 DONTADDTORECENT
@@ -167,6 +168,7 @@ roundf
 RSHIFT
 SACL
 schandle
+SEH
 semver
 serializer
 SETVERSION
@@ -214,6 +216,7 @@ UOI
 UPDATEINIFILE
 userenv
 USEROBJECTFLAGS
+Vcpp
 Viewbox
 virtualalloc
 vsnwprintf

src/cascadia/PublicTerminalCore/HwndTerminalAutomationPeer.cpp

@@ -5,6 +5,7 @@
 #include "HwndTerminalAutomationPeer.hpp"
 #include "../../types/UiaTracing.h"
 #include <UIAutomationCoreApi.h>
+#include <delayimp.h>
 
 #pragma warning(suppress : 4471) // We don't control UIAutomationClient
 #include <UIAutomationClient.h>
@@ -13,6 +14,15 @@ using namespace Microsoft::Console::Types;
 
 static constexpr wchar_t UNICODE_NEWLINE{ L'\n' };
 
+static int CheckDelayedProcException(int exception) noexcept
+{
+    if (exception == VcppException(ERROR_SEVERITY_ERROR, ERROR_PROC_NOT_FOUND))
+    {
+        return EXCEPTION_EXECUTE_HANDLER;
+    }
+    return EXCEPTION_CONTINUE_SEARCH;
+}
+
 // Method Description:
 // - creates a copy of the provided text with all of the control characters removed
 // Arguments:
@@ -123,6 +133,12 @@ void HwndTerminalAutomationPeer::SignalCursorChanged()
 
 void HwndTerminalAutomationPeer::NotifyNewOutput(std::wstring_view newOutput)
 {
+    if (_notificationsUnavailable) [[unlikely]]
+    {
+        // What if you tried to notify, but God said no
+        return;
+    }
+
     // Try to suppress any events (or event data)
     // that is just the keypress the user made
     auto sanitized{ Sanitize(newOutput) };
@@ -155,5 +171,19 @@ void HwndTerminalAutomationPeer::NotifyNewOutput(std::wstring_view newOutput)
 
     const auto sanitizedBstr = wil::make_bstr_nothrow(sanitized.c_str());
     static auto activityId = wil::make_bstr_nothrow(L"TerminalTextOutput");
-    LOG_IF_FAILED(UiaRaiseNotificationEvent(this, NotificationKind_ActionCompleted, NotificationProcessing_All, sanitizedBstr.get(), activityId.get()));
+    _tryNotify(sanitizedBstr.get(), activityId.get());
+}
+
+// This needs to be a separate function because it is using SEH try/except, which
+// is incompatible with C++ unwinding
+void HwndTerminalAutomationPeer::_tryNotify(BSTR string, BSTR activity)
+{
+    __try
+    {
+        LOG_IF_FAILED(UiaRaiseNotificationEvent(this, NotificationKind_ActionCompleted, NotificationProcessing_All, string, activity));
+    }
+    __except (CheckDelayedProcException(GetExceptionCode()))
+    {
+        _notificationsUnavailable = true;
+    }
 }

src/cascadia/PublicTerminalCore/HwndTerminalAutomationPeer.hpp

@@ -38,5 +38,7 @@ public:
     void NotifyNewOutput(std::wstring_view newOutput) override;
 #pragma endregion
 private:
+    void _tryNotify(BSTR string, BSTR activity);
     std::deque<wchar_t> _keyEvents;
+    bool _notificationsUnavailable{};
 };

src/cascadia/PublicTerminalCore/PublicTerminalCore.vcxproj

@@ -57,7 +57,8 @@
        instead of APISet forwarders for easier Windows 7 compatibility. -->
   <ItemDefinitionGroup>
     <Link>
-      <AdditionalDependencies>Uiautomationcore.lib;onecoreuap.lib;%(AdditionalDependencies)</AdditionalDependencies>
+      <AdditionalDependencies>delayimp.lib;Uiautomationcore.lib;onecoreuap.lib;%(AdditionalDependencies)</AdditionalDependencies>
+      <DelayLoadDLLs>uiautomationcore.dll;%(DelayLoadDLLs)</DelayLoadDLLs>
     </Link>
   </ItemDefinitionGroup>
 </Project>