Fix ToolsLocator to work with Gradle 6.1 Instant Execution

[eskatos]

This PR fixes ToolsLocator to comply with Gradle's Instant Execution constraints.

See https://gradle.github.io/instant-execution/ for more information about what Instant Execution is.

The PR also enables test coverage for Gradle 6.1 and adds more coverage for using Instant Execution on a Java project.

The Android support isn't fixed for Instant Execution by this PR. I'll consider working on it afterwards. Having support for Java projects would already be awesome.

[voidzcy]

I am wondering why only this change is needed to enable Instant Execution. Isn't migrating to configuration avoidance APIs a prerequisite?

[eskatos]

Configuration avoidance is orthogonal to instant execution. This change is required because heavyweight Configuration instances can't be serialized by instant execution whereas FileCollection instances do work.

[voidzcy]

Thanks for making this enhancement.

[eskatos]

Hi, any chance we can get a plugin release with this fix?

[voidzcy]

Looks like this is the only change since previous release. We might make a release after having more significant changes.

[eskatos]

It's been a bit more than a month and no other change got merged. Any chance you could consider releasing this improvement in a patch release? We and other teams are blocked on this.

[davidburstrom]

A new release would unblock one of our workstreams, so it'd be appreciated!

[voidzcy]

Sure, I will do a release recently.

[voidzcy]

0.8.12 is released and is available on maven central and Gradle plugin portal.