Problem: Fast context for msg_show event inhibits vim.ui_attach from
displaying a stream of messages from a single command.
Solution: Remove fast context from msg_show events emitted as a result
of explicit API/command calls. The fast context was originally
introduced to prevent issues with internal messages.
- Move all generator Lua scripts to the `src/gen/`
- Add a `.luarc.json` to `src/gen/`
- Add a `preload.lua` to `src/gen/`
- Add `src` to `package.path` so it aligns with `.luarc.json'
- Fix all `require` statements in `src/gen/` so they are consistent:
- `require('scripts.foo')` -> `require('gen.foo')`
- `require('src.nvim.options')` -> `require('nvim.options')`
- `require('api.dispatch_deprecated')` -> `require('nvim.api.dispatch_deprecated')`
