Fix build script to avoid jvm plugin applied

[chao2zhang]

This addresses #3345.

Why moving the script back to root build.gradle? (Partially reverting #2621)

According to Gradle official doc, buildSrc is being imported as included build. buildSrc is useful for pinning versions for common dependencies, or defining tasks or plugins that are shareable across multiple projects.

Although common.gradle.kts has kotlin("jvm") apply false, when root build.gradle applies the plugin common from buildSrc, koltin("jvm") is still applied. This behavior caused the issue in #3345 that Kotlin/JVM gradle plugin is applied to the root project.

Test

Before: https://scans.gradle.com/s/vetym5o5m7fj6 577 tasks
After: https://gradle.com/s/5w5rmu7is7vyk 572 tasks

Out of scope

This PR only solves a limited problem for Kotlin/JVM gradle plugin being applied to the root build.gradle. There are still other scripts like packaging, releasing, and detekt in the buildSrc. There are still top-level tasks registered, like :jar, :detekt etc.

[codecov]

Codecov Report

Merging #3389 (7443ffd) into master (a7efff2) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #3389   +/-   ##
=========================================
  Coverage     80.46%   80.46%           
  Complexity     2739     2739           
=========================================
  Files           448      448           
  Lines          8282     8282           
  Branches       1573     1573           
=========================================
  Hits           6664     6664           
  Misses          771      771           
  Partials        847      847           

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