Expose WindowsTerminalBranding to the preprocessor (optionally) (#7986)

Our build pipeline was originally set up such that we could take any
binaries from the Terminal build and seamlessly re-package them with the
release or preview livery. My initial plan was to stamp a stable and
preview build at the same time, out of the same bits, to make ring
promotion easier.

I've never done that. For the last five releases, we've just re-cut a
new stable build along with the new preview build, usually because we
want to backport some fixes to stable.

This commit introduces preprocessor defines, detectable through CL and
RC, for any project that wants them. Right now, that's just going to be
WindowsTerminal.vcxproj (since it hosts the icons and the app entry
point). This list may be extended to include wt (the shim executable)
and the shell extension at some future date.

This will greatly simplify the logic in #7971, as we'll no longer need
to detect if we're dev or preview at runtime. It may also simplify the
logic in the shell extension for determining whether we're Dev or not.

build/rules/Branding.targets

@@ -0,0 +1,18 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project ToolsVersion="14.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <PropertyGroup>
+    <_WTBrandingPreprocessorToken Condition="'$(WindowsTerminalBranding)'=='Preview'">WT_BRANDING_PREVIEW</_WTBrandingPreprocessorToken>
+    <_WTBrandingPreprocessorToken Condition="'$(WindowsTerminalBranding)'=='Release'">WT_BRANDING_RELEASE</_WTBrandingPreprocessorToken>
+    <_WTBrandingPreprocessorToken Condition="'$(_WTBrandingPreprocessorToken)'==''">WT_BRANDING_DEV</_WTBrandingPreprocessorToken>
+  </PropertyGroup>
+
+  <ItemDefinitionGroup>
+    <ClCompile>
+      <PreprocessorDefinitions>$(_WTBrandingPreprocessorToken);%(PreprocessorDefinitions)</PreprocessorDefinitions>
+    </ClCompile>
+
+    <ResourceCompile>
+      <PreprocessorDefinitions>$(_WTBrandingPreprocessorToken);%(PreprocessorDefinitions)</PreprocessorDefinitions>
+    </ResourceCompile>
+  </ItemDefinitionGroup>
+</Project>

src/cascadia/WindowsTerminal/WindowsTerminal.vcxproj

@@ -155,6 +155,7 @@
     <!-- **END VC LIBS HACK** -->
   </Target>
 
+  <Import Project="$(OpenConsoleDir)\build\rules\Branding.targets" />
   <Import Project="$(OpenConsoleDir)\build\rules\GenerateSxsManifestsFromWinmds.targets" />
   <Import Project="..\..\..\packages\Terminal.ThemeHelpers.0.2.200324001\build\native\Terminal.ThemeHelpers.targets" Condition="Exists('..\..\..\packages\Terminal.ThemeHelpers.0.2.200324001\build\native\Terminal.ThemeHelpers.targets')" />
 </Project>