; Merge from origin/emacs-27

The following commits were skipped:

b99848c72c Bind default-directory to the project root
19534f988c Make sure default-directory relates to the originating buffer
d1455027e0 Initialize signal descriptions after pdumping
256356a36f Clarify the "Sentinels" node in the lispref manual
89f1634afc Fix problem with non-ASCII characters in nnmaildir