<AWT Dev> RFR: 8250856 Address reliance on default constructors in the AWT APIs

[Sergey Bylokhov]

Hello.
Please review the fix for jdk/client.

Bug: https://bugs.openjdk.java.net/browse/JDK-8250856
CSR: https://bugs.openjdk.java.net/browse/JDK-8251211
Fix: http://cr.openjdk.java.net/~serb/8250856/webrev.00

This is part of a larger effort to remove reliance of default
constructors in the JDK's exported API in preparation for introduction
of a lint warning for this situation.

This fix adds default public constructors to the public non-abstract
classes and protected constructors to the public abstract classes.

-- 
Best regards, Sergey.