Improve build logic for Kotlin (#1520)

- Enforce Kotlin version via resolution rule (replaces BOM)
  - fail if kotlin-stdlib/kotlin-reflect exceed target version
- Replace kotlin-stdlib-jdk8 with kotlin-stdlib (jdk7/8 are now shims)
- Port pkl-core annotation processor to Java (with Codex)
- removes kotlin-stdlib from its compile classpath for better dependency
hygiene (Java module)
- Downgrade clikt for Kotlin 2.2 compatibility
- Upgrade kotlinx-serialization

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Co-authored-by: Daniel Chao <dan.chao@apple.com>

stdlib/gradle.lockfile

@@ -1,6 +1,5 @@
 # This is a Gradle generated file for dependency locking.
 # Manual edits can break the build and are not advised.
 # This file is expected to be part of source control.
-org.jetbrains.kotlin:kotlin-bom:2.2.21=pklFormatter
 org.jspecify:jspecify:1.0.0=pklFormatter
 empty=signatures