Introduce KotlinVersion API

#KT-14789

libraries/stdlib/src/kotlin/util/KotlinVersion.kt

@@ -0,0 +1,65 @@
+package kotlin
+
+/**
+ * Represents a version of the Kotlin standard library
+ */
+public class KotlinVersion(val major: Int, val minor: Int, val patch: Int) : Comparable<KotlinVersion> {
+    public constructor(major: Int, minor: Int) : this(major, minor, 0)
+
+    private val version = versionOf(major, minor, patch)
+
+    private fun versionOf(major: Int, minor: Int, patch: Int): Int {
+        require(major in 0..99 && minor in 0..99 && patch in 0..99) { "Version components are out of range: $major.$minor.$patch" }
+        return major * 100 * 100 + minor * 100 + patch
+    }
+
+    /**
+     * Returns the integer representation of this version.
+     *
+     * Integer representations of two [KotlinVersion] instances can be compared,
+     * so that if `v1.toInt() > v2.toInt()` then `v1 > v2`.
+     *
+     * This value should not be persisted, as it can change between program runs.
+     */
+    public fun toInt(): Int = version
+
+    /**
+     * Returns the string representation of this version
+     */
+    override fun toString(): String = "$major.$minor.$patch"
+
+    override fun equals(other: Any?): Boolean {
+        if (this === other) return true
+        val otherVersion = (other as? KotlinVersion) ?: return false
+        return this.version == otherVersion.version
+    }
+
+    override fun hashCode(): Int = version
+
+    override fun compareTo(other: KotlinVersion): Int = version - other.version
+
+    public fun isAtLeast(major: Int, minor: Int): Boolean =
+            // or this.version >= versionOf(major, minor, 0)
+            this.major > major || (this.major == major &&
+                    this.minor >= minor)
+
+    public fun isAtLeast(major: Int, minor: Int, patch: Int): Boolean =
+            // or this.version >= versionOf(major, minor, patch)
+            this.major > major || (this.major == major &&
+                    (this.minor > minor || this.minor == minor &&
+                            this.patch >= patch))
+
+    public fun isAtLeast(version: KotlinVersion): Boolean = this >= version
+
+    companion object {
+        /**
+         * Returns the current version of the Kotlin standard library
+         */
+        // TODO: get from metadata or hardcode automatically during build
+        @kotlin.jvm.JvmField
+        public val CURRENT: KotlinVersion = KotlinVersion(1, 1, 0)
+
+        // should we have 'parse'?
+
+    }
+}