RFR: 8336382: Fixes error reporting in loading AWT and fonts

[Karm Michal Babacek]

If there is a problem with finding and calling e.g. `java/awt/GraphicsEnvironment` in `AWTIsHeadless`, the env' Exception remains set and it is not cleared. Later, that manifests as:

    Fatal error reported via JNI: Could not allocate library name

Which is misleading. The code path is perhaps rare in a normal JDK usage, but it has been complicating our users' bug reports in the GraalVM/native-image ecosystem for quite some time.

Instead of failing later indicating that the user has incorrectly configured JNI, it bails out very soon with a message that seems as if a jstring could not have been allocated. It sends users on wild goose chases where it appears `JNU_NewStringPlatform` calls failed,  e.g.

* https://github.com/oracle/graal/issues/9138
* https://github.com/oracle/graal/issues/8475
* https://github.com/oracle/graal/issues/9300
* https://github.com/quarkusio/quarkus/issues/31596
* https://github.com/graalvm/mandrel/issues/292
* https://github.com/Karm/mandrel-integration-tests/issues/262

This commit fixes the error reporting in the AWTIsHeadless.

Furthermore, when AOT compiled, there is little sense for having a JAVA_HOME, yet some parts of AWT code look for it to search fonts. In such case, an empty directory structure is enough to accommodate it, e.g.

/tmp/JAVA_HOME/
/tmp/JAVA_HOME/conf
/tmp/JAVA_HOME/conf/fonts
/tmp/JAVA_HOME/lib

The exception is somewhat cryptic for users again, merely stating:

    Exception in thread "main" java.io.IOException: Problem reading font data.
        at java.desktop at 22.0.1/java.awt.Font.createFont0(Font.java:1205)
        at java.desktop at 22.0.1/java.awt.Font.createFont(Font.java:1076)
        at imageio.Main.loadFonts(Main.java:139

Adding the cause there makes it clearer, i.e. that JAVA_HOME might be missing:

    Exception in thread "main" java.io.IOException: Problem reading font data.
        at java.desktop at 23-internal/java.awt.Font.createFont0(Font.java:1206)
        at java.desktop at 23-internal/java.awt.Font.createFont(Font.java:1076)
        at imageio.Main.loadFonts(Main.java:139)
        at imageio.Main.paintRectangles(Main.java:97)
        at imageio.Main.main(Main.java:195)
        at java.base at 23-internal/java.lang.invoke.LambdaForm$DMH/sa346b79c.invokeStaticInit(LambdaForm$DMH)
    Caused by: java.lang.Error: java.home property not set
        at java.desktop at 23-internal/sun.awt.FontConfiguration.findFontConfigFile(FontConfiguration.java:180)
        at java.desktop at 23-internal/sun.awt.FontConfiguration.<init>(FontConfiguration.java:97)

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Commit messages:
 - Fixes error reporting in loading AWT and fonts

Changes: https://git.openjdk.org/jdk/pull/20169/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20169&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8336382
  Stats: 10 lines in 2 files changed: 9 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/20169.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20169/head:pull/20169

PR: https://git.openjdk.org/jdk/pull/20169