Problem:
`vim.lsp.buf.[implementation|definition|...]({ reuse_win = true })` does not
jump cursor to existing window if buffer is already open.
Steps to reproduce:
1. `nvim repro.lua`
2. Insert anything that lsp can read to open the library definition/implementation, e.g., `vim.keymap.set`
3. open `repro.lua` buffer and the library buffer side by side.
4. type `gd` over `set` to jump to the library definition.
The open buffer is scrolled to the target line, but cursor does not jump.
Solution:
Call nvim_set_current_win if necessary.
(cherry picked from commit 6926fc1615)
2435d72283