docs(Either): describe the all method

this adds documentation to the `all` method, and
moves it closer to the very similar, but subtly
different `exists` function.

Fixes N/A

arrow-libs/core/arrow-core/src/commonMain/kotlin/arrow/core/Either.kt

@@ -881,6 +881,22 @@ public sealed class Either<out A, out B> {
   public inline fun exists(predicate: (B) -> Boolean): Boolean =
     fold({ false }, predicate)
 
+  /**
+   * Returns `true` if [Left] or returns the result of the application of
+   * the given predicate to the [Right] value.
+   *
+   * Example:
+   * ```
+   * Right(12).all { it > 10 } // Result: true
+   * Right(7).all { it > 10 }  // Result: false
+   *
+   * val left: Either<Int, Int> = Left(12)
+   * left.all { it > 10 }      // Result: false
+   * ```
+   */
+  public inline fun all(predicate: (B) -> Boolean): Boolean =
+    fold({ true }, predicate)
+
   /**
    * Returns the right value if it exists, otherwise null
    *
@@ -946,9 +962,6 @@ public sealed class Either<out A, out B> {
       is Left -> null
     }
 
-  public inline fun all(predicate: (B) -> Boolean): Boolean =
-    fold({ true }, predicate)
-
   public fun isEmpty(): Boolean = isLeft
 
   public fun isNotEmpty(): Boolean = isRight