Expose some font utility API for public usage

DEVSIX-5101

Author: Artyom Yanchevsky

kernel/src/main/java/com/itextpdf/kernel/font/DocTrueTypeFont.java

@@ -58,11 +58,11 @@ This file is part of the iText (R) project.
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-class DocTrueTypeFont extends TrueTypeFont implements IDocFontProgram {
+public class DocTrueTypeFont extends TrueTypeFont implements IDocFontProgram {
 
     private static final long serialVersionUID = 4611535787920619829L;
 
-	private PdfStream fontFile;
+    private PdfStream fontFile;
     private PdfName fontFileName;
     private PdfName subtype;
     private int missingWidth = 0;

kernel/src/main/java/com/itextpdf/kernel/font/FontUtil.java

@@ -63,10 +63,19 @@ This file is part of the iText (R) project.
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-class FontUtil {
+public class FontUtil {
 
     private static final HashMap<String, CMapToUnicode> uniMaps = new HashMap<>();
 
+    public static String addRandomSubsetPrefixForFontName(final String fontName) {
+        final StringBuilder newFontName = new StringBuilder(fontName.length() + 7);
+        for (int k = 0; k < 6; ++k) {
+            newFontName.append((char) (Math.random() * 26 + 'A'));
+        }
+        newFontName.append('+').append(fontName);
+        return newFontName.toString();
+    }
+
     static CMapToUnicode processToUnicode(PdfObject toUnicode) {
         CMapToUnicode cMapToUnicode = null;
         if (toUnicode instanceof PdfStream) {

kernel/src/main/java/com/itextpdf/kernel/font/PdfFont.java

@@ -492,11 +492,7 @@ protected boolean isWrappedObjectMustBeIndirect() {
      */
     protected static String updateSubsetPrefix(String fontName, boolean isSubset, boolean isEmbedded) {
         if (isSubset && isEmbedded) {
-            StringBuilder s = new StringBuilder(fontName.length() + 7);
-            for (int k = 0; k < 6; ++k) {
-                s.append((char) (Math.random() * 26 + 'A'));
-            }
-            return s.append('+').append(fontName).toString();
+            return FontUtil.addRandomSubsetPrefixForFontName(fontName);
         }
         return fontName;
     }