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"
        }
      )
 <

runtime/lua/vim/lsp/handlers.lua

@@ -317,7 +317,9 @@ end
 --- 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"
 ---   }
 --- )
 --- </pre>

runtime/lua/vim/lsp/util.lua

@@ -1050,6 +1050,13 @@ function M.make_floating_popup_options(width, height, opts)
     col = 1
   end
 
+  local title = (opts.border and opts.title) and opts.title or nil
+  local title_pos
+
+  if title then
+    title_pos = opts.title_pos or 'center'
+  end
+
   return {
     anchor = anchor,
     col = col + (opts.offset_x or 0),
@@ -1061,6 +1068,8 @@ function M.make_floating_popup_options(width, height, opts)
     width = width,
     border = opts.border or default_border,
     zindex = opts.zindex or 50,
+    title = title,
+    title_pos = title_pos,
   }
 end