Fix instrumented eval-defun not printing "Edebug:" to the echo area

Fix instrumented eval-defun not printing "Edebug:" to the echo area

* lisp/progmodes/elisp-mode.el (elisp--eval-defun): Determine if we're
instrumenting a function and call eval-region with PRINTFLAG set to
nil if so (Bug#50245).

* test/lisp/progmodes/elisp-mode-tests.el
(eval-defun-prints-edebug-when-instrumented): Add a new test.