Remove data race for marksweep block lists

[qinsoon]

This PR refactors mark sweep.

• It removes the data race for accessing block lists, as discussed in Block cell size is sometimes zero in native MarkSweep #1103 (comment).
• It fixes an issue that block state did not get reset before GC and caused marked blocks to stay alive forever: Mimalloc/marksweep high memory overhead #688 (comment)
• It fixes an issue that empty blocks did not get released for lazy sweeping.

[wks]

I added some comments. One strange thing is that once a Block becomes BlockState::Marked, it remain marked forever. But I think the block state of all marked blocks should be reset to unmarked so that we can find blocks that actually have marked objects.

[wks]

Style check failed due to trailing spaces. If you use VSCode, there are extensions for highlighting trailing spaces and removing them.

[wks]

The field BlockList::lock and its methods BlockList::lock() and BlockList::unlock() are unused. We can remove them now.

[qinsoon]

The field BlockList::lock and its methods BlockList::lock() and BlockList::unlock() are unused. We can remove them now.

I kept the methods just in case we may need them in the future.

[wks]

LGTM