Fix #3316: javalib FileChannel append behavior now matches a JVM

[LeeTibbert]

Fix #3316

javalib FileChannel write & position methods now more closely match JVM behavior.

[LeeTibbert]

End of session: 1 build error. I will check for other build errors next session.

To the tune of "It ain't me, babe":

" Run tests Windows / Test experimental multithreading support (3, debug, boehm, none) (pull_request) Failing after 17m"

"""
[error] Test org.scalanative.testsuite.javalib.lang.ObjectMonitorTest.keeps recursions track after wait when already inflated failed: java.lang.AssertionError: done, took 3.603 sec
[error] at java.lang.StackTrace$.currentStackTrace$$anonfun$1(Unknown Source)
[error] at java.lang.StackTrace$$$Lambda$2.applyVoid(Unknown Source)
[error] at scala.runtime.function.JProcedure1.apply(Unknown Source)
[error] at scala.scalanative.unsafe.Zone$.apply(Unknown Source)
[error] at java.lang.StackTrace$.currentStackTrace(Unknown Source)
[error] at java.lang.Throwable.fillInStackTrace(Unknown Source)
"""