Rethink format task approach

[Tapchicoma]

Currently format tasks works the same as common lint tasks, except that they may modify inputs. This leads to the several problems with this tasks caching: #302 or #194

Possible solutions to this problem:

• actually run lint tasks first, don't fail the tasks, then run format only on files with files violations. Format task is never cacheable, but uses lint tasks reports as input.
• something else?

@JLLeitschuh maybe something else comes to your mind how to solve it as well?

[JLLeitschuh]

Diffplug spotless solved this, somehow. @nedtwigg do you have any insights here?

[nedtwigg]

You can make the format task incremental / up-to-date-able, but there are a few tricky corner cases. The high level is here, the actual implementation is everything that touches this little class.

[vlsi]

There's an alternative option for Gradle 5.4+ (it uses org.gradle.work.InputChanges): https://github.com/autostyle/autostyle/blob/90a40e3523a5344cdc127f031bc986bb4102bdb7/plugin-gradle/src/main/kotlin/com/github/autostyle/gradle/AutostyleApplyTask.kt#L65

[JLLeitschuh]

@Tapchicoma what are your thoughts on @vlsi's suggestion here?