Update shadow plugin 6.1.0 -> 7.1.1

Version 7.1.1 is absent in jcenter, so additional repository was added
in some modules.

Leave old version in NewMultiplatformIT.kt because of
`This version of Shadow supports Gradle 7.0+ only. Please upgrade.` error.

^KTI-733 Fixed

kotlin-native/build.gradle

@@ -41,11 +41,12 @@ buildscript {
             mavenCentral()
             jcenter()
         }
+        gradlePluginPortal()
     }
 
     dependencies {
         //classpath project(":kotlin-native-utils")
-        classpath 'com.github.jengelman.gradle.plugins:shadow:5.1.0'
+        classpath 'gradle.plugin.com.github.johnrengelman:shadow:7.1.1'
     }
 }
 import org.jetbrains.kotlin.konan.*