[gdb/tui] Fix secondary prompt

With CLI, a session defining a command looks like:
...
(gdb) define foo
Type commands for definition of "foo".
End with a line saying just "end".
>bar
>end
(gdb)
...

With TUI however, we get the same secondary prompts, and type the same, but
are left with:
...
(gdb) define foo
Type commands for definition of "foo".
End with a line saying just "end".
(gdb)
...

Fix this by calling tui_inject_newline_into_command_window in
gdb_readline_wrapper_line, as is done in tui_command_line_handler.

Tested on x86_64-linux.

PR tui/30636
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30636

gdb/testsuite/gdb.tui/secondary-prompt.exp

@@ -0,0 +1,38 @@
+# Copyright 2023 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+require allow_tui_tests
+
+tuiterm_env
+
+Term::clean_restart 24 80
+
+if {![Term::enter_tui]} {
+    unsupported "TUI not supported"
+    return
+}
+
+# Define a macro.
+send_gdb "define foo\n"
+send_gdb "bar\n"
+send_gdb "end\n"
+
+# Wait for the last secondary prompt to appear, followed by the gdb prompt.
+Term::wait_for ">end"
+
+# Regression test for PR tui/30636.  Make sure the secondary prompts are not
+# overwritten.
+Term::check_region_contents "secondary prompt not overwritten" 0 19 80 2 \
+    "^>bar *\r\n>end *$"

gdb/top.c

@@ -77,6 +77,7 @@
 
 #if defined(TUI)
 # include "tui/tui.h"
+# include "tui/tui-io.h"
 #endif
 
 #ifndef O_NOCTTY
@@ -958,6 +959,11 @@ gdb_readline_wrapper_line (gdb::unique_xmalloc_ptr<char> &&line)
   saved_after_char_processing_hook = after_char_processing_hook;
   after_char_processing_hook = NULL;
 
+#if defined(TUI)
+  if (tui_active)
+    tui_inject_newline_into_command_window ();
+#endif
+
   /* Prevent parts of the prompt from being redisplayed if annotations
      are enabled, and readline's state getting out of sync.  We'll
      reinstall the callback handler, which puts the terminal in raw