[dotnet] Fix dependencies for Microsoft.<platform>.Sdk.DefaultItems.p…

…rops. (#20478)

Make sure Microsoft.\<platform\>.Sdk.DefaultItems.props is rebuilt if the
current hash changes.

This fixes a local rebuild issue, where we'd rebuild
Microsoft.\<platform\>.Sdk.Versions.props, but not
Microsoft.\<platform\>.Sdk.DefaultItems.props.

A build failure like this would thus result:

    tools/msbuild/iOS/Xamarin.Shared.targets(606,3): error : A bundle identifier is required. Either add an 'ApplicationId' property in the project file, or add a 'CFBundleIdentifier' entry in the project's Info.plist file.

because:

* We store the current git hash in both of the files mentioned above.
* We only include default items in a build if the git hashes match.
* Since the files weren't both rebuilt, they'd contain different hashes, and
  thus we wouldn't include Info.plist in the build, leading to the build
  error.

dotnet/Makefile

@@ -145,7 +145,7 @@ endef
 $(foreach platform,$(DOTNET_PLATFORMS),$(eval $(call AutoImports,$(platform))))
 
 define DefaultItems
-Microsoft.$1.Sdk/targets/Microsoft.$1.Sdk.DefaultItems.props: targets/Microsoft.Sdk.DefaultItems.template.props Makefile
+Microsoft.$1.Sdk/targets/Microsoft.$1.Sdk.DefaultItems.props: targets/Microsoft.Sdk.DefaultItems.template.props Makefile $(TOP)/Make.config.inc $(GIT_DIRECTORY)/HEAD $(GIT_DIRECTORY)/index
 	$$(Q_GEN) sed \
 		-e "s/@PLATFORM@/$1/g" \
 		-e "s/@TARGET_FRAMEWORK_VERSION@/$(subst net,,$(DOTNET_TFM))/g" \