Clean up GC_Finalizable*Buffer classes code

[dmitripivkine]

Use correct types, fix formatting

[dmitripivkine]

fixes #20458

[amicic]

do we care about spaces after the comma (I think most of the time we have them)?

	GC_FinalizableReferenceBuffer(MM_GCExtensions *extensions) :
		_head(NULL)
		,_tail(NULL)
		,_count(0)
		,_extensions(extensions)

[dmitripivkine]

yes, good point. I am going to fix it.

[dmitripivkine]

fixed

[amicic]

jenkins compile aix jdk17

[LinHu2016]

LGTM

[keithc-ca]

I think this pattern is an improvement: it reads better, additions or removals (at the end) don't change any other lines, but I suggest the first field should line up with the rest by moving the colon:

	GC_FinalizableClassLoaderBuffer(MM_GCExtensions *extensions)
		: _head(NULL)
		, _tail(NULL)
		, _count(0)
		, _extensions(extensions)
	{}