Add accessor methods for SharedSecrets#javaObjectInputFilterAccess

[gayanW]

Adds SharedSecrets#getJavaObjectInputFilterAccess and SharedSecrets#setJavaObjectInputFilterAccess methods to jdk.internal.misc.SharedSecrets model class.

This fixes:

[junit] java.lang.NoSuchMethodException:
        jdk.internal.misc.SharedSecrets.setJavaObjectInputFilterAccess(Ljdk/internal/misc/JavaObjectInputFilterAccess;)V

Fixes: #111

[cyrille-artho]

Same as with the previous issue: should this code initialize a singleton, or possibly return null, if (javaObjectInputFilterAccess == null)?

[gayanW]

Our ensureClassInitialized method seems to do nothing. So it will possibly return null.

jpf-core/src/classes/modules/java.base/jdk/internal/misc/Unsafe.java

Line 215 in 09c442c

public native void ensureClassInitialized(Class<?> cls);

jpf-core/src/peers/gov/nasa/jpf/vm/JPF_jdk_internal_misc_Unsafe.java

Lines 260 to 264 in 09c442c

	@MJI
	public void ensureClassInitialized__Ljava_lang_Class_2__V (MJIEnv env, int unsafeRef, int clsObjRef) {
	// <2do> not sure if we have to do anyting here - if we have a class object, the class should already
	// be initialized
	}

JDK source for ensureClassInitialized:
https://github.com/unofficial-openjdk/openjdk/blob/6caf29475edb2d25cb9349f763451e20aa545c74/src/java.base/share/classes/jdk/internal/misc/Unsafe.java#L1032-L1043

[cyrille-artho]

I see, this is indeed the same as in the JDK implementation. Merging this one.