GC and versionVector handling in documents created after v0.5.6

[hackerwins]

What happened:

Starting from v0.5.6, there was a change where the browser is now able to deactivate the client during the beforeunload in CodePair, leading to GC being processed.

However, when testing documents created after v0.5.6, the following issues were observed:

• Executing doc.getGarbageLen() on documents created after v0.5.6 appears to correctly remove garbage under normal conditions.
• However, there are discrepancies in the sizes of doc.changeID.versionVector and doc.presences. Occasionally, versionVector does not decrease, while presences appear to be cleaned up correctly.

What you expected to happen:

The expectation is that GC should function correctly for both documents created after v0.5.6, ensuring that both doc.presences and versionVector maintain corresponding sizes.

How to reproduce it (as minimally and precisely as possible):

https://codepair.yorkie.dev/hackerwins/674522059b55661e04668721/share?token=c5uq0y

Anything else we need to know?:

Related to #723

Environment:

• Operating system: All
• Browser and version: All
• Yorkie version (use yorkie version): v0.5.6
• Yorkie JS SDK version: v0.5.6