Upgrade Kotlin to 1.8.20 (#4753)

Summary:
[android] Upgrade Kotlin to 1.8.20
The additional source/target settings should hopefully no longer be necessary with
AGP 8.1:

https://kotlinlang.org/docs/gradle-configure-project.html#gradle-java-toolchains-support

Pull Request resolved: https://github.com/facebook/flipper/pull/4753

Test Plan:
- CI
- Build sample app
- AS sync

 ---
Stack created with [Sapling](https://sapling-scm.com). Best reviewed with [ReviewStack](https://reviewstack.dev/facebook/flipper/pull/4753).
* https://github.com/facebook/flipper/issues/4759
* https://github.com/facebook/flipper/issues/4758
* https://github.com/facebook/flipper/issues/4757
* https://github.com/facebook/flipper/issues/4756
* https://github.com/facebook/flipper/issues/4755
* https://github.com/facebook/flipper/issues/4754
* __->__ https://github.com/facebook/flipper/issues/4753
* https://github.com/facebook/flipper/issues/4752
* https://github.com/facebook/flipper/issues/4751

Reviewed By: ivanmisuno

Differential Revision: D46068906

Pulled By: passy

fbshipit-source-id: 93da60ebfe2ec590ef88ea1936fcfd5257699cc7

android/plugins/leakcanary2/build.gradle

@@ -19,6 +19,11 @@ android {
         targetSdkVersion rootProject.targetSdkVersion
     }
 
+    compileOptions {
+        targetCompatibility rootProject.javaTargetVersion
+        sourceCompatibility rootProject.javaTargetVersion
+    }
+
     dependencies {
         compileOnly "org.jetbrains.kotlin:kotlin-stdlib:$KOTLIN_VERSION"
         implementation project(':android')

android/plugins/litho/build.gradle

@@ -18,6 +18,11 @@ android {
         targetSdkVersion rootProject.targetSdkVersion
     }
 
+    compileOptions {
+        targetCompatibility rootProject.javaTargetVersion
+        sourceCompatibility rootProject.javaTargetVersion
+    }
+
     dependencies {
         compileOnly deps.lithoAnnotations
         implementation project(':android')

android/plugins/retrofit2-protobuf/build.gradle

@@ -19,6 +19,11 @@ android {
         targetSdkVersion rootProject.targetSdkVersion
     }
 
+    compileOptions {
+        targetCompatibility rootProject.javaTargetVersion
+        sourceCompatibility rootProject.javaTargetVersion
+    }
+
     dependencies {
         implementation "org.jetbrains.kotlin:kotlin-stdlib:$KOTLIN_VERSION"
         implementation project(':android')