feat(diagnostic): config.status #36693

Problem:
`diagnostic.status()` is configured via `config.signs`, but users may
want diagnostics only in statusline, not in the gutter (signs).

Solution:
Add `config.status`.

test/functional/lua/diagnostic_spec.lua

@@ -4097,10 +4097,10 @@ describe('vim.diagnostic', function()
       )
     end)
 
-    it('uses text from diagnostic.config().signs.text[severity]', function()
+    it('uses text from diagnostic.config().status.text[severity]', function()
       local result = exec_lua(function()
         vim.diagnostic.config({
-          signs = {
+          status = {
             text = {
               [vim.diagnostic.severity.ERROR] = '⨯',
               [vim.diagnostic.severity.WARN] = '⚠︎',