Enable WINRT_LEAN_AND_MEAN (#15215)

`WINRT_LEAN_AND_MEAN` removes a bunch of less often used parts of the
C++/WinRT headers:

- `std::hash` specializations for every object
- `operator <<(ostream)` overloads for any `IStringable`
- Interface producers for interfaces that are marked "exclusive"

There's only one place where we were using even one of these.

Enabling this saves us (optimistically) 30 seconds of build time on the
CI agents and shrinks our largest PCH (TerminalApp, x64, Debug) by about
150MiB.

It's not huge, but it's not nothing.

src/cascadia/TerminalApp/CommandPalette.h

@@ -7,6 +7,8 @@
 #include "CommandPalette.g.h"
 #include "AppCommandlineArgs.h"
 
+#include <til/hash.h>
+
 // fwdecl unittest classes
 namespace TerminalAppLocalTests
 {
@@ -60,6 +62,14 @@ namespace winrt::TerminalApp::implementation
         TYPED_EVENT(PreviewAction, Windows::Foundation::IInspectable, Microsoft::Terminal::Settings::Model::Command);
 
     private:
+        struct winrt_object_hash
+        {
+            size_t operator()(const auto& value) const noexcept
+            {
+                return til::hash(winrt::get_abi(value));
+            }
+        };
+
         friend struct CommandPaletteT<CommandPalette>; // for Xaml to bind events
 
         Windows::Foundation::Collections::IVector<winrt::TerminalApp::FilteredCommand> _allCommands{ nullptr };
@@ -141,7 +151,7 @@ namespace winrt::TerminalApp::implementation
         void _choosingItemContainer(const Windows::UI::Xaml::Controls::ListViewBase& sender, const Windows::UI::Xaml::Controls::ChoosingItemContainerEventArgs& args);
         void _containerContentChanging(const Windows::UI::Xaml::Controls::ListViewBase& sender, const Windows::UI::Xaml::Controls::ContainerContentChangingEventArgs& args);
         winrt::TerminalApp::PaletteItemTemplateSelector _itemTemplateSelector{ nullptr };
-        std::unordered_map<Windows::UI::Xaml::DataTemplate, std::unordered_set<Windows::UI::Xaml::Controls::Primitives::SelectorItem>> _listViewItemsCache;
+        std::unordered_map<Windows::UI::Xaml::DataTemplate, std::unordered_set<Windows::UI::Xaml::Controls::Primitives::SelectorItem, winrt_object_hash>, winrt_object_hash> _listViewItemsCache;
         Windows::UI::Xaml::DataTemplate _listItemTemplate;
 
         friend class TerminalAppLocalTests::TabTests;

src/cppwinrt.build.pre.props

@@ -73,6 +73,8 @@
       <DisableSpecificWarnings>5104;28204;%(DisableSpecificWarnings)</DisableSpecificWarnings>
 
       <AdditionalUsingDirectories>$(WindowsSDK_WindowsMetadata);$(AdditionalUsingDirectories)</AdditionalUsingDirectories>
+
+      <PreprocessorDefinitions>WINRT_LEAN_AND_MEAN;%(PreprocessorDefinitions)</PreprocessorDefinitions>
     </ClCompile>
     <Link>
       <SubSystem Condition="'%(SubSystem)'==''">Console</SubSystem>