Prevent illegal access exceptions, when retrieving options for private library interfaces with an instance field

[fkistner]

System info

1. Version of JNA and related jars: latest master
2. Version and vendor of the java virtual machine: Amazon Corretto 11.0.9.1
3. Operating system: macOS 10.15.7 (19H2)
4. System architecture (CPU type, bitness of the JVM): x86_64

JNA encounters IllegalAccessExceptions, when trying to retrieve library options from private Library interfaces that contain an instance field. Since direct mapped classes may retrieve options for the first time, only when a callback is passed or returned, this can happen rather unexpectedly.

This change suppresses the IllegalAccessExceptions by calling setAccessible like it is already done, when looking up other fields of the library interface via reflection.

Example stack traces (see PrivateLibraryInfoTest.java and PrivateDirectCallbacksTest.java)

java.lang.IllegalArgumentException: Could not access instance of interface com.sun.jna.different_package.PrivateDirectCallbacksTest$PrivateWithCallbackArgumentTestLibrary (java.lang.IllegalAccessException: Class com.sun.jna.Native can not access a member of class com.sun.jna.different_package.PrivateDirectCallbacksTest$PrivateWithCallbackArgumentTestLibrary with modifiers "public static final")

	at com.sun.jna.Native.loadLibraryInstance(Native.java:673)
	at com.sun.jna.Native.getLibraryOptions(Native.java:737)
	at com.sun.jna.CallbackReference.getFunctionPointer(CallbackReference.java:455)
	at com.sun.jna.different_package.PrivateDirectCallbacksTest$DirectPrivateWithCallbackArgumentTestLibrary.callVoidCallback(Native Method)

java.lang.ExceptionInInitializerError
	at com.sun.jna.different_package.PrivateDirectCallbacksTest$PrivateWithCallbackReturnTestLibrary.<clinit>(PrivateDirectCallbacksTest.java:39)
	at com.sun.jna.different_package.PrivateDirectCallbacksTest.testInvokeCallback(PrivateDirectCallbacksTest.java:63)
…
Caused by: java.lang.IllegalArgumentException: Could not access instance of interface com.sun.jna.different_package.PrivateDirectCallbacksTest$PrivateWithCallbackReturnTestLibrary (java.lang.IllegalAccessException: Class com.sun.jna.Native can not access a member of class com.sun.jna.different_package.PrivateDirectCallbacksTest$PrivateWithCallbackReturnTestLibrary with modifiers "public static final")
	at com.sun.jna.Native.loadLibraryInstance(Native.java:673)
	at com.sun.jna.Native.getLibraryOptions(Native.java:737)
	at com.sun.jna.Native.getTypeMapper(Native.java:799)
	at com.sun.jna.Structure$FFIType.get(Structure.java:2151)
	at com.sun.jna.Structure$FFIType.get(Structure.java:2146)
	at com.sun.jna.Native.register(Native.java:1793)

[matthiasblaesing]

Merged via 578220e - thank you!