Merge from origin/emacs-26

Merge from origin/emacs-26

6415b2d Allow read-passwd to hide characters inserted by C-y.  (Secur...
8cb4ffb * etc/PROBLEMS: Document issues with double-buffering.  (Bug#...
fd10070 * lisp/window.el (window-largest-empty-rectangle): Fix grammar.
e1a4403 Minor changes in the Emacs manual
372fda6 Improve the "Files" chapter of the Emacs manual
9afc86d Improve the "Search" chapter of the Emacs manual
22f98b3 * src/indent.c (Findent_to): Doc fix.  (Bug#30260)
085ee43 Improve documentation of 'edebug-defun'
4dd1b33 Mention crashes due to Noto Serif Kannada fonts