The maximum signed value on 32-bit systems is 2 ^ 31 - 1. When using 2 ^ 31 for
the default timeout, the value would overflow on such systems resulting in
a negative value, which caused a stack trace when calling wait() without
a timeout.

Fixes #30846

Fixes #31107

- Also fix `vim.validate()` for PUC Lua when showing errors for values
  that aren't string or number.

Problem:
vim.ui.open "locks up" Nvim if the spawned process does not terminate. #27986

Solution:
- Change `vim.ui.open()`:
    - Do not call `wait()`.
    - Return a `SystemObj`. The caller can decide if it wants to `wait()`.
- Change `gx` to `wait()` only a short time.
    - Allows `gx` to show a message if the command fails, without the
      risk of waiting forever.

Problem:
Processing non-fast events during SystemObj:wait() may cause two pieces
of code to interfere with each other, and is different from jobwait().

Solution:
Don't process non-fast events during SystemObj:wait().

Typings introduced in #26032 and #26552 have a few conflicts, so we
merge and clean them up. We also fix some incorrect type annotation in
the `vim.lsp.rpc` package. See the associated PR for more details.

Summary:

- vim.rpc.Dispatchers -> vim.lsp.rpc.Dispatchers
- vim.lsp.rpc.Error -> lsp.ResponseError
- Revise docs

Added a lpeg grammar for LuaCATS and use it in lua2dox.lua