Migrate to Kotlin 2.3.20

[landomen]

Task/Issue URL: https://app.asana.com/1/137249556945/project/1214119362406643/task/1214799610249614?focus=true
Tech Design URL (if applicable): N/A

Description

• Bump versions (versions.properties): version.kotlin 2.2.21 → 2.3.20; KSP 2.2.21-2.0.5 → 2.3.7 (both KSP lines; KSP moved to a decoupled version scheme — 2.3.7 is the build aligned to Kotlin 2.3.20).
• Bump Metro language level (build.gradle:283-284): Metro-mode languageVersion/apiVersion KOTLIN_2_2 → KOTLIN_2_3.
• Fix Dagger metadata reader (app/build.gradle): add kapt "org.jetbrains.kotlin:kotlin-metadata-jvm:2.3.20" — Dagger 2.57.2's reader caps at metadata 2.2.0 but 2.3.20 emits 2.3.0 (:app KAPT only). Dagger itself not bumped (even 2.59.2 ships a 2.2.x reader).
• Fix 28 LV-2.3 compile errors (explicit type args): reified-type-param-inferred-to-intersection became an error at LV 2.3 — combine<Any, Unit>(...) in InputScreenViewModel.kt, arrayOf(...) ×26 in JsonRulesMapperTest.kt, arrayOf(...) in WideEventsMigration1To2Test.kt.
• Keep Metro at 1.0.1 for now, bump in separate PR

Steps to test this PR

Smoke check

• Verify unit and Android tests pass for both DI variants
• Verify e2e tests pass for both DI variants
• 1) Metro: https://github.com/duckduckgo/Android/actions/runs/27945052008
• 2) Anvil: https://github.com/duckduckgo/Android/actions/runs/27950202725
• Verify privacy tests pass for both DI variants
• 1) Metro: https://github.com/duckduckgo/Android/actions/runs/27944967007
• 2) Anvil: https://github.com/duckduckgo/Android/actions/runs/27947878923
• Install build and smoke check the app

UI changes

No UI changes

---

Note

Medium Risk
Wide toolchain bump (Kotlin/KSP/compiler settings) affects every module and both DI build variants; fixes are compile-time only but full CI and smoke testing is important.

Overview
Bumps Kotlin to 2.3.20 and KSP to 2.3.7 in versions.properties, and sets Metro dual-build languageVersion / apiVersion to Kotlin 2.3 in the root build.gradle.

Adds a :app-only kapt dependency on kotlin-metadata-jvm:2.3.20 so Dagger’s annotation processor can read Kotlin 2.3 @Metadata without upgrading Dagger itself.

Fixes Kotlin 2.3 compile errors from stricter generic inference: explicit type arguments on combine<Any, Unit> in InputScreenViewModel, arrayOf<MatchingAttribute> in JsonRulesMapperTest, and arrayOf<Any> in WideEventsMigration1To2Test. No intended runtime behavior changes.

^{Reviewed by Cursor Bugbot for commit fb63c1c. Bugbot is set up for automated code reviews on this repo. Configure here.}