feat(lsp): support set title in lsp relate floatwindow (#21110)

runtime/doc/lsp.txt

@@ -1330,7 +1330,9 @@ hover({_}, {result}, {ctx}, {config})               *vim.lsp.handlers.hover()*
      vim.lsp.handlers["textDocument/hover"] = vim.lsp.with(
        vim.lsp.handlers.hover, {
          -- Use a sharp border with `FloatBorder` highlights
-         border = "single"
+         border = "single",
+         -- add the title in hover float window
+         title = "hover"
        }
      )
 <