This commit removes the use of the incubating PropertyState and
Provider API that was introduced in Gradle 4.0 and deprecated in
Gradle 4.3. A not-deprecated-but-still-incubating replacement was
introduced in Gradle 4.3. The short life of PropertyState and Provider
has made me wary of using an incubating Gradle API in our public API
as it may not be stable for long. Therefore, this commit does not move
to the replacement as it is incubating. Instead, it falls back to
using Gradle's convention mapping. This is internal API, but its use
is not part of our public API and I perceive the risk of using it to
be lower than using the deprecated and/or incubating API alternatives.

Closes gh-11640