feat(clipboard): enable OSC 52 clipboard provider by default (#26064)

Use the XTGETTCAP sequence to determine if the host terminal supports
the OSC 52 sequence and, if it does, enable the OSC 52 clipboard
provider by default.

This is only done automatically when all of the following are true:

  1. Nvim is running in the TUI
  2. 'clipboard' is not set to unnamed or unnamedplus
  3. g:clipboard is unset
  4. Nvim is running in an SSH connection ($SSH_TTY is set)
  5. Nvim is not running inside tmux ($TMUX is unset)

runtime/plugin/osc52.lua

@@ -0,0 +1,37 @@
+local tty = vim.iter(vim.api.nvim_list_uis()):any(function(ui)
+  return ui.chan == 1 and ui.stdout_tty
+end)
+
+if
+  not tty
+  or vim.g.clipboard ~= nil
+  or vim.o.clipboard ~= ''
+  or not os.getenv('SSH_TTY')
+  or os.getenv('TMUX')
+then
+  return
+end
+
+require('vim.termcap').query('Ms', function(cap, seq)
+  assert(cap == 'Ms')
+
+  -- If the terminal reports a sequence other than OSC 52 for the Ms capability
+  -- then ignore it. We only support OSC 52 (for now)
+  if not seq:match('^\027%]52') then
+    return
+  end
+
+  local osc52 = require('vim.ui.clipboard.osc52')
+
+  vim.g.clipboard = {
+    name = 'OSC 52',
+    copy = {
+      ['+'] = osc52.copy('+'),
+      ['*'] = osc52.copy('*'),
+    },
+    paste = {
+      ['+'] = osc52.paste('+'),
+      ['*'] = osc52.paste('*'),
+    },
+  }
+end)