[Feature Request] Reduce code analyzer's suggestion messages.

**Is your feature request related to a problem? Please describe.**
When building docfx solution.
Currently about 2918 messages are shown on Visual Studio `Error List` window (When enable Build + Intellisense).

I want to reduce this `suggestion messages` because a lot of unneeded suggestions are reported.
And want to change some useful suggestion message level to warning. (e.g, performance related rules.)

**Describe the solution you'd like**
It needs following tasks to reduce suggestion messages.
- Fix code by refactoring
- Suppress message by code comment
- Suppress unrequired message by changing log level with `.editorconfig` settings.

I'll send PR to fix this issue.