revert: "fix(lsp): use buffer scheme for files not stored on disk" (#22604)

Although using `buffer://` for unsaved file buffers fixes issues with
language servers like eclipse.jdt.ls or ansible-language-server, it
breaks completion and signature help for clangd.

A regression is worse than a fix for something else, so this reverts
commit 896d672736.

The spec change is also still in dicussion, see
https://github.com/microsoft/language-server-protocol/pull/1679#discussion_r1130704886

runtime/lua/vim/lsp/util.lua

@@ -2032,12 +2032,7 @@ end
 ---@returns `TextDocumentIdentifier`
 ---@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocumentIdentifier
 function M.make_text_document_params(bufnr)
-  bufnr = bufnr or 0
-  local uri = vim.uri_from_bufnr(bufnr)
-  if not uv.fs_stat(api.nvim_buf_get_name(bufnr)) then
-    uri = uri:gsub('^file://', 'buffer://')
-  end
-  return { uri = uri }
+  return { uri = vim.uri_from_bufnr(bufnr or 0) }
 end
 
 --- Create the workspace params
@@ -2070,7 +2065,7 @@ function M.make_formatting_params(options)
     insertSpaces = vim.bo.expandtab,
   })
   return {
-    textDocument = M.make_text_document_params(0),
+    textDocument = { uri = vim.uri_from_bufnr(0) },
     options = options,
   }
 end