fix(lsp): ensure buffers are re-attached on rename (#16266)

If a LSP server sent a workspace edit containing a rename the buffers
file name changed without the server receiving a close notification for
the old buffer and without the client properly re-attaching on the new
file.

This affected `Move` code-actions in nvim-jdtls, but also
`vim.lsp.buf.rename` on a class level.

test/functional/plugin/lsp_spec.lua

@@ -1735,6 +1735,7 @@ describe('LSP', function()
 
         -- after rename the target file must have the contents of the source file
         local bufnr = vim.fn.bufadd(new)
+        vim.fn.bufload(new)
         return vim.api.nvim_buf_get_lines(bufnr, 0, -1, true)
       ]], old, new)
       eq({'Test content'}, lines)