HexFormat 'fromHex' methods should be static

A number of HexFormat methods converting from strings to numbers do not use delimiter, prefix, suffix, and uppercase parameters and would be more convenient if the methods were static.

   public boolean isHexDigit(int);
   public int fromHexDigit(int);
   public int fromHexDigits(java.lang.CharSequence);
   public int fromHexDigits(java.lang.CharSequence, int, int);
   public long fromHexDigitsToLong(java.lang.CharSequence);
   public long fromHexDigitsToLong(java.lang.CharSequence, int, int);