feat: resolve projects by lockDatabase

[Myriad-Dreamin]

Although we have great multiple-files project support in VS Code, we still experiment a sample implementation in VS Code. The new mechanism is put behind a flag. It isn't enabled by default. You can also only use the lockDatabase in some specific workspaces.

• the CLI or server will update the lock file if one invokes compile/preview commands via CLI or LSP.
• the server will see the lock file to see what's the best main file to use:
  • If a file is depended by some unique main file recorded in the lock, the main file is used.
  • If a file is depended by multiple main files, the most recently recorded main file wins.
  • otherwise, the language server sets the main file to the file itself.

Even if there is no any editor-side (client-side) additional support, people should be able to tell such information to the language server by invoking CLI in terminal.

We might deprecate the pin/unpin commands if this solution receives positive voice after experiment.