Handling Proper Defaulting of BuildTargetingString within nested templates

[scbedd]

We want to ensure that setting a BuildTargetingString at queue time is available. This enables us to exclude problematic packages from a run when attempting to release another package in the same service.

Of course, the ideal is that we never have any red pipelines, but the fact of the matter is sometimes random stuff crops up.

The original "solution" that I came up with is not working properly. I thought I had tested it, but obviously I missed something during verification.

The core problem is that the way that parameters resolve. Parameters are resolved at compile time, so even if you set up something at the very top level of your build yaml like I linked above:

While within this template scope we can use $(BuildTargetingStringValue). If we pass that to another template, it immediately reverts to the default parameter argument. For reasons of how the templates are compiled.

This PR just recognizes and deals with that fact. So essentially:

1. Run the resolve-targeting-string.yml if you need to use resolved BuildTargetingString in your current template. After running template resolve-targeting-string.yml, just reference to the coalesced value by $(TargetingString)
2. Otherwise, just pass ${{ paramters.BuildTargetingString }} to other template calls. Given that resolution will default anyway, might as well make it explicit.

Once resolve-targeting-string.yml runs once in the build, it won't run again.

Test Runs

• UnTargeted, Standard is the standard build for this PR.
• Targeted, Standard
• Untargeted, Daily Dev
• Targeted, Daily Dev

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[scbedd]

Just at the top of each job.