Merge coreservice & chainservice

[CoderZhi]

Description

Merging coreservice and chainservice. Quite a few features inside of chainservice may not be appropriate, but it is out of the scope of this PR. In addition:

1. Move integrity tests to api/integrity/, and delete some tests which are not supposed to be in integrity test.
2. Modify MemKVStore in db/kvstore_impl.go for test purpose. (Reimplementation of MemKVStore is a TODO)

Fixes #2875

Type of change

Please delete options that are not relevant.

• [ ] New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• [ ] Unit Test
• [ ] Minicluster

Test Configuration:

• Firmware version:
• Hardware:
• Toolchain:
• SDK:

Checklist:

• [ ] My code follows the style guidelines of this project
• [ ] I have performed a self-review of my code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [ ] My changes generate no new warnings
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] New and existing unit tests pass locally with my changes
• [ ] Any dependent changes have been merged and published in downstream modules