Implicit params being propogated to Refs

[wlynch]

Expected Behavior

Implicit params should only be available with the same resource - they shouldn't be considered for references.

Actual Behavior

From @sbwsg in #4388 (comment):

Just to add another anecdotal here - we experienced some surprising behaviour in relation to this change during the release of 0.32 of Tekton Pipelines. One of our Pipelines relied on a default param value in a referenced Task, which was then unexpectedly overridden by the implicit param defined in the Pipeline.

It's tricky to describe in words, here's a link to the PipelineTask as we had it before we noticed this behaviour and here's a link to the PipelineTask after we corrected for it.

^ In the first link we don't pass the platforms param because we're relying on the default defined in the referenced Task. With implicit params that platforms param gets overridden with the value in the platforms param defined for the Pipeline. The reason for the difference in the values is a bit nuanced but regardless it looks like this might be accidentally backwards incompatible?

edit: tried to disambiguate that the default was set in the referenced task.

Additional Info

Likely affected code:

pipeline/pkg/apis/pipeline/v1beta1/pipeline_defaults.go

Lines 44 to 47 in 1401ab7

	if config.FromContextOrDefaults(ctx).FeatureFlags.EnableAPIFields == "alpha" {
	ctx = addContextParams(ctx, pt.Params)
	ps.Tasks[i].Params = getContextParams(ctx, pt.Params...)
	}

[wlynch]

/assign