Add the ability to create custom report variants

[shanshin]

Motivation

• it is necessary to generate reports for classes located in the same project and related to the JVM target and several specific android build variants
• it is necessary to generate merged reports on classes from different subprojects of the same build, while some of these subprojects contain JVM classes, other classes from different Android build variants
• reports should be generated for classes in such combinations that must be defined by the user himself

Terminology

Report variant - named set of sources and tests grouped by certain conditions: JVM target, Android build variant, their commbination, etc.). It is acceptable to generate reports for each variant.

Solution

A special DSL will be added to create custom report variant that can be filled with classes from JVM target, Android build variants and other custom variants:

// configure report variants (creating custom variants and exports it)
koverVariants {
    // create custom reports variant
    create("customVariantName") {
        // add android or custom report variants
        add("jvm", "apiRelease", "appRelease", "libRelease")

        // flexibly add android variants
        addAndroid(buildType = "release", "api", "app", "lib") // for Android build variants `apiRelease`, `appRelease`, `libRelease`
        // also
        addAndroid(buildType = "release", "*") // for Android build variants `release`, `apiRelease`, `appRelease`, `libRelease`
    }
}

[shanshin]

Implemented in 0.8.0-Beta.
This is not a production ready release, the plugin DSL is experimental and can be changed after receiving feedback.

[mgroth0]

Hey @shanshin , is there a typesafe way to add all variants from the build, without having to rely on strings?