Deprecate constructor Charsets.Charsets() to be private in 4.0

Author: garydgregory

src/changes/changes.xml

@@ -49,6 +49,7 @@ The <action> type attribute can be add,update,fix,remove.
     <release version="2.19.0" date="YYYY-MM-DD" description="Version 2.18.1: Java 8 is required.">
       <!-- FIX -->
       <action dev="ggregory" type="fix"                due-to="Gary Gregory">Deprecate constructor Counters.Counters() to be private in 4.0.</action>
+      <action dev="ggregory" type="fix"                due-to="Gary Gregory">Deprecate constructor Charsets.Charsets() to be private in 4.0.</action>
       <!-- ADD -->
       <action dev="ggregory" type="add" issue="IO-860" due-to="Nico Strecker, Gary Gregory">Add ThrottledInputStream.Builder.setMaxBytes(long, ChronoUnit).</action>
       <action dev="ggregory" type="add"                due-to="Gary Gregory">Add IOIterable.</action>

src/main/java/org/apache/commons/io/Charsets.java

@@ -218,4 +218,14 @@ public static Charset toCharset(final String charsetName) throws UnsupportedChar
     public static Charset toCharset(final String charsetName, final Charset defaultCharset) throws UnsupportedCharsetException {
         return charsetName == null ? defaultCharset : Charset.forName(charsetName);
     }
+
+    /**
+     * Construct a new instance.
+     *
+     * @deprecated Will be private in 4.0
+     */
+    @Deprecated
+    public Charsets() {
+        // empty
+    }
 }