bug#41087: 27.0.91; How to remove Emacs 27 changes to minibuffer?

[Drew Adams <drew.adams@oracle.com>]

NEWS says this:

** Minibuffer

+++
*** A new user option, 'minibuffer-beginning-of-buffer-movement', has
been introduced to allow controlling how the 'M-<' command works in
the minibuffer.  If non-nil, point will move to the end of the prompt
(if point is after the end of the prompt).

+++
*** When the minibuffer is active, echo-area messages are displayed at
the end of the minibuffer instead of hiding the minibuffer by the echo
area display.  The new user option 'minibuffer-message-clear-timeout'
controls how messages displayed in this situation are removed from the
minibuffer.

---
*** Minibuffer now uses 'minibuffer-message' to display error messages
at the end of the active minibuffer.

+++
*** 'y-or-n-p' now uses the minibuffer to read 'y' or 'n' answer.

---
*** Some commands that previously used 'read-char-choice' now read
a character using the minibuffer by 'read-char-from-minibuffer'.


Emacs 27 is unfortunately _totally_ unusable for me.  Cannot do the
slightest thing.

I think that some of the problems come from the changes to minibuffer
and echo-area behavior.  Regardless of whether that is the case, I want
to undo those changes.  Is there an option for that? (I hope so.)  If
not, what changes do I need to make from Lisp, to get back the prior
behavior?



In GNU Emacs 27.0.91 (build 1, x86_64-w64-mingw32)
 of 2020-04-20
Repository revision: c36c5a3dedbb2e0349be1b6c3b7567ea7b594f1c
Windowing system distributor `Microsoft Corp.', version 10.0.18362
Configured using:
 `configure --without-dbus --host=x86_64-w64-mingw32
 --without-compress-install 'CFLAGS=-O2 -static''