refactor: prepare sendrequest and move to internalSendAsync

[tisonkun]

This refers to #1071. This follows up to #1118.

1. Factor out updateSchema
2. Factor out updateUncompressedPayload
3. Factor out updateMetaData
4. Factor out updateChunkInfo
5. Move all these methods (expect updateChunkInfo which we will handle resource later) to internalSendAsync so that we populate the sendrequest in application thread
6. Drop stopBlock

Does this pull request potentially affect one of the following parts:

If yes was chosen, please highlight the changes

• Dependencies (does it add or upgrade a dependency): (yes / no)
• The public API: (yes / no)
• The schema: (yes / no / don't know)
• The default values of configurations: (yes / no)
• The wire protocol: (yes / no)

Documentation

• Does this pull request introduce a new feature? (yes / no)
• If yes, how is the feature documented? (not applicable / docs / GoDocs / not documented)
• If a feature is not applicable for documentation, explain why?
• If a feature is not documented yet in this PR, please create a followup issue for adding the documentation

[wolfstudy]

Good refactor, LGTM +1

[tisonkun]

Merging...

I'm rebasing #1121 onto this patch to fix two resource management issues with a unsplittable refactor.