Use generics for providers API

Using generics for the providers API allows a type to be associated
with a ProviderKey, resulting in a type-safe API without that doesn't
require runtime type assertions by every caller.

Unfortunately, Go does not allow generic types in methods, only in
functions [1].  This prevents a type-safe API on ModuleContext, and
requires moving the API to be functions that take a ModuleContext as
a parameter.

This CL creates the new API, but doesn't convert all of the callers.

[1] https://go.googlesource.com/proposal/+/refs/heads/master/design/43651-type-parameters.md#no-parameterized-methods)

Bug: 316410648
Test: builds
Change-Id: I3e30d68b966b730efd968166a38a25cc144bd6de

bloaty/bloaty.go

@@ -26,7 +26,7 @@ const bloatyDescriptorExt = ".bloaty.csv"
 const protoFilename = "binary_sizes.pb.gz"
 
 var (
-	fileSizeMeasurerKey blueprint.ProviderKey
+	fileSizeMeasurerKey blueprint.ProviderKey[measuredFiles]
 	pctx                = android.NewPackageContext("android/soong/bloaty")
 
 	// bloaty is used to measure a binary section sizes.