[ci] Fix maestro publishing for stable packages

[pjcollins]

We've seen the build promotion pipeline fail when trying to publish
stable package versions:

error : Package 'Microsoft.iOS.Ref.net8.0_17.5' has stable version '17.5.8001' but is targeted at a non-isolated feed 'https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet8/nuget/v3/index.json'

This is because we were not declaring these packages as stable when
building the build asset registry manifest.

Fix this by passing the $(IsStableBuild) property to the build asset
manifest creation task. This property needs to be updated manually when
switching to stable package versioning (see commit 4ea5dbb).

When $(IsStableBuild) is set to true, packages will be pushed to an
isolated feed during publishing, such as:

  Package Microsoft.Android.Ref.34@34.0.125 (Shipping) should go to https://pkgs.dev.azure.com/dnceng/public/_packaging/darc-pub-dotnet-android-b8317b6f/nuget/v3/index.json (Isolated, Public)

[pjcollins]

Tested this by rebuilding the manifest for some .NET 8 stable packs with $(IsStableBuild)=true, and manually trying to add that build to the "General Testing" channel: https://dev.azure.com/devdiv/DevDiv/_build/results?buildId=9898256&view=logs&j=ba23343f-f710-5af9-782d-5bd26b102304&t=74531eb2-9b39-5603-839e-94e3ba212b65

This is only relevant for recent .NET 9 publishing changes, and does not need to be backported.

[jonathanpeppers]

I was comparing what we have on the release/8.0.2xx branch:

android/Directory.Build.props

Lines 32 to 41 in 36bbac0

	<!-- NuGet package version numbers. See Documentation/guides/OneDotNet.md.
	Rules:
	* Major/Minor match Android stable API level, such as 30.0 for API 30.
	* Bump first digit of the patch version for feature releases (and reset the first two digits to 0)
	-->
	<AndroidPackVersion>34.0.1</AndroidPackVersion>
	<AndroidPackVersionPatchIndex>$(AndroidPackVersion.LastIndexOf("."))</AndroidPackVersionPatchIndex>
	<AndroidPackVersionMajorMinor>$(AndroidPackVersion.Substring(0,$(AndroidPackVersionPatchIndex)))</AndroidPackVersionMajorMinor>
	<AndroidPackVersionPatch>$(AndroidPackVersion.Substring($([MSBuild]::Add($(AndroidPackVersionPatchIndex), 1))))</AndroidPackVersionPatch>
	<AndroidPackVersionSuffix>rtm</AndroidPackVersionSuffix>

Could this check $(AndroidPackVersionSuffix) == 'rtm' to determine true or false?

[pjcollins]

That sounds reasonable to me, I think it would be best to not introduce more properties that need to be manually tweaked when stablizing.

I was looking at AndroidPackVersionSuffix and I think it's not used anywhere when moving to stable package versions? I don't think that's an issue, we'll just have to make sure to still update it to rtm each time even though it won't be referenced by anything?

[jonathanpeppers]

Let's just leave $(AndroidPackVersionSuffix) as-is, if it wasn't doing anything.