Add update-kotlin-version skill to automate repetitive steps in multiple files (JetBrains#2920)

## Testing
N/A

## Release Notes
N/A

Author: eymar

ai-skills/update-kotlin-version/SKILL.md

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+---
+name: update-kotlin-version
+description: This skill should be used when the user asks to "update Kotlin version", "upgrade Kotlin", "change Kotlin to X.Y.Z", or mentions updating the Kotlin compiler version in the project.
+version: 1.0.0
+---
+
+# Update Kotlin Version — Compose Multiplatform Core
+
+This skill helps update the Kotlin version across the project. The process involves updating several files to ensure consistency.
+
+## Important Rule
+
+`JETBRAINS_COMPILE_KOTLIN_VERSION` must not be the latest version, but rather the newest - 1. For example, if we use Kotlin 2.3.20 as the latest, `JETBRAINS_COMPILE_KOTLIN_VERSION` should be `KOTLIN_2_2`.
+
+## Required Information
+
+Before starting, ask the user for:
+- The target Kotlin version (e.g., "2.3.20")
+
+## Update Process
+
+Perform the following steps in order:
+
+### 1. Update `gradle/libs.versions.toml`
+
+Update three main entries in the `[versions]` section:
+
+a. **Update `composeCompilerPlugin`** to the new Kotlin version:
+```toml
+composeCompilerPlugin = "X.Y.Z"
+```
+
+b. **Update `kotlin`** to the new Kotlin version:
+```toml
+kotlin = "X.Y.Z"
+```
+
+c. **Update or add patch versions** (under the comment `# Use the most up-to-date patch`):
+- If a version entry for this major.minor already exists (e.g., `kotlin23` for 2.3.x), update it
+- If this is a new major.minor version, add a new entry (e.g., `kotlin24 = "2.4.Z"`)
+
+Example:
+```toml
+# Use the most up-to-date patch
+kotlin21 = "2.1.20"
+kotlin22 = "2.2.20"
+kotlin23 = "2.3.20"
+kotlin = "2.3.20"
+```
+
+### 2. Update `buildSrc/public/src/main/kotlin/org/jetbrains/androidx/build/JetBrainsCompatibilityVersions.kt`
+
+Update `JETBRAINS_COMPILE_KOTLIN_VERSION` to be the **previous major.minor version**, not the latest:
+
+```kotlin
+val JETBRAINS_COMPILE_KOTLIN_VERSION = KOTLIN_X_Y
+```
+
+For example:
+- If updating to Kotlin 2.3.20, set to `KOTLIN_2_2`
+- If updating to Kotlin 2.4.0, set to `KOTLIN_2_3`
+
+### 3. Check `buildSrc/public/src/main/kotlin/androidx/build/AndroidXConfiguration.kt`
+
+If this is a new major.minor version (e.g., moving from 2.3 to 2.4):
+
+a. Add a new enum entry in the `KotlinTarget` enum:
+```kotlin
+KOTLIN_2_4(KotlinVersion.KOTLIN_2_4, "kotlin24"),
+```
+
+b. Update the `LATEST` entry to point to the new version:
+```kotlin
+LATEST(KOTLIN_2_4);
+```
+
+If this is just a patch update (e.g., 2.3.10 → 2.3.20), no changes are needed in this file.
+
+### 4. Verify the Changes
+
+After making all updates:
+1. Confirm that `JETBRAINS_COMPILE_KOTLIN_VERSION` is set to the previous major.minor version, not the latest
+2. Verify that all three version entries in `libs.versions.toml` are updated consistently
+3. If a new major.minor version was added, confirm the `KotlinTarget` enum includes it
+
+## Key Files
+
+- `gradle/libs.versions.toml` - Version catalog with Kotlin versions
+- `buildSrc/public/src/main/kotlin/org/jetbrains/androidx/build/JetBrainsCompatibilityVersions.kt` - Compatibility version settings
+- `buildSrc/public/src/main/kotlin/androidx/build/AndroidXConfiguration.kt` - Kotlin target configuration (updated only for new major.minor versions)