RFR: 8273581: Change the mechanism by which JDK loads the platform-specific FontManager class [v6]

[Alexander Zvegintsev]

On Mon, 20 Sep 2021 11:26:13 GMT, Alexander Scherbatiy <alexsch at openjdk.org> wrote:

>> FontManagerFactory class uses reflection to load platform specific FontManager classes from "sun.font.fontmanager" property.
>> 
>> Fix proposes creating FontManager platform specific classes directly in the similar way as it has been already done for GraphicsEnvironment and AWT Toolkit ([JDK-8130266](https://bugs.openjdk.java.net/browse/JDK-8130266) and [JDK-8212700](https://bugs.openjdk.java.net/browse/JDK-8212700)).
>> 
>> FontManager is internal jdk class. It is placed in `sun.font` package and java modularization encapsulates  FontManager from subclassing and using by a user.
>> 
>> The fix reuses PlatformGraphicsInfo to create FontManager platform specific classes. May be FontManager creation code needs to be placed in its own info classes.
>
> Alexander Scherbatiy has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Use Double-check idiom for lazy initialization of instance fields with local variable
>  - Remove unnecessary explicit initialization of volatile variable

Marked as reviewed by azvegint (Reviewer).

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PR: https://git.openjdk.java.net/jdk/pull/5517