Option to pack jars as uber JAR, support Proguard for uber JAR

[badmannersteam]

Proposed changes

1. Added support to join JARs to the uber JAR with ProGuard, disabled by default:

compose.desktop {
    application {
        buildTypes.release.proguard {
            joinOutputJars.set(true)
        }
    }
}

2. All 'release' tasks now really depend on ProGuard, as stated in tutorial.

Testing

• A new auto test

• Manual:

1. Test on Windows/macOs/Linux
2. Test the new Gradle parameter joinOutputJars:

compose.desktop {
    application {
        buildTypes.release.proguard {
            joinOutputJars.set(true)
        }
    }
}

false (by default) should generate multiple jars (except for package*UberJarForCurrentOS)
true should generate a single jar in a result distribution
3. Test debug tasks:

run
runDistributable
createDistributable
packageUberJarForCurrentOS

4. Test release tasks:

runRelease
runReleaseDistributable
createReleaseDistributable
packageReleaseUberJarForCurrentOS

The jars should be reduced in size (because Proguard is enabled in the release mode)

This should be test by QA.

Issues fixed

Fixes #4129

[terrakok]

@badmannersteam could you add integration tests for that?

[badmannersteam]

@terrakok probably yes, but what configuration combinations they should check?

[terrakok]

I would expect a multi-module project + proguard as uberjar and a regular multi-module project

[badmannersteam]

Added some tests.

[badmannersteam]

@terrakok seems like that all for now.

[terrakok]

LGTM

[badmannersteam]

I'll check the tests today and also want to fix the issue on Windows, that was mentioned above (by flattering into the intermediate jar instead of directory).

[terrakok]

@badmannersteam could you check failed tests and rebase the branch on top of the master?

[badmannersteam]

@terrakok all done.

[badmannersteam]

@igordmn, look at this pls :)

[badmannersteam]

@terrakok @igordmn
I apologize for being intrusive, but are there any chances that this will be merged before the next release?
Just want to know for proper planning.

[igordmn]

Most probably yes, it will be in the next release (1.6.10).

I plan to review it soon.

[igordmn]

Thanks!

LGTM.

Few things:

1. I changed the title/description by our new PR format
2. I moved README to support/1.6.10, which will be merged to master on the release date