Add 6 standard charsets.

libraries/stdlib/src/kotlin/text/CharsetsJVM.kt

@@ -0,0 +1,44 @@
+package kotlin
+
+import java.nio.charset.*
+import kotlin.platform.*
+
+/**
+ * Constant definitions for the standard [charsets](Charset). These
+ * charsets are guaranteed to be available on every implementation of the Java
+ * platform.
+ */
+public object Charsets {
+    /**
+     * Eight-bit UCS Transformation Format
+     */
+    // TODO: KT-5766 Cannot compile function with optional parameters with platformStatic value
+    public val UTF_8: Charset = Charset.forName("UTF-8")
+
+    /**
+     * Sixteen-bit UCS Transformation Format, byte order identified by an
+     * optional byte-order mark
+     */
+    public val UTF_16: Charset = Charset.forName("UTF-16")
+
+    /**
+     * Sixteen-bit UCS Transformation Format, big-endian byte order
+     */
+    public val UTF_16BE: Charset = Charset.forName("UTF-16BE")
+
+    /**
+     * Sixteen-bit UCS Transformation Format, little-endian byte order
+     */
+    public val UTF_16LE: Charset = Charset.forName("UTF-16LE")
+
+    /**
+     * Seven-bit ASCII, a.k.a. ISO646-US, a.k.a. the Basic Latin block of the
+     * Unicode character set
+     */
+    public val US_ASCII: Charset = Charset.forName("US-ASCII")
+
+    /**
+     * ISO Latin Alphabet No. 1, a.k.a. ISO-LATIN-1
+     */
+    public val ISO_8859_1: Charset = Charset.forName("ISO-8859-1")
+}