Make LookupContext#closeables thread safe

[oehme]

This collection is modified by multiple threads, e.g. the FastTerminal setup thread calling context.closeables.add(out::flush). This can result in closeables being lost and can make subsequent builds with the embedded runner fail.

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[oehme]

I found this while investigating the logging stackoverflows which we are still getting on a daily basis with Maven 4.x. I got a lucky break today and found a build where it didn't stackoverflow, but instead failed here:

Caused by: java.lang.ArrayIndexOutOfBoundsException: Index 1 out of bounds for length 0
    at java.base/java.util.ArrayList.add(ArrayList.java:484)
    at java.base/java.util.ArrayList.add(ArrayList.java:496)
    at org.apache.maven.cling.invoker.LookupInvoker.doCreateTerminal(LookupInvoker.java:344)
    at org.apache.maven.cling.invoker.LookupInvoker.lambda$createTerminal$5(LookupInvoker.java:316)
    at org.apache.maven.jline.MessageUtils.lambda$systemInstall$0(MessageUtils.java:55)
    at org.apache.maven.jline.FastTerminal.lambda$new$0(FastTerminal.java:55)

I suspect this may be the cause for the stackoverflows, because with the right timing, the arraylist#add could succed and overwrite another closeable in the list.

[github-actions]

@gnodet Please assign appropriate label to PR according to the type of change.