PR mi/18833 gdb.execute ("set param value", to_string=True) will crash gdb if using MI

PR mi/18833 gdb.execute ("set param value", to_string=True) will crash gdb if using MI

gdb/ChangeLog:

	* cli/cli-logging.c (pop_output_files): Don't restore redirection
	if MI-like.
	* mi/mi-out.c: #include "vec.h".
	(ui_filep): New type.
	(DEV_VEC_P (ui_filep)): New type.
	(struct ui_out_data) <buffer, original_buffer>: Delete.
	(struct ui_out_data) <streams>: New member.
	(mi_ui_out_impl): Add data_destroy field.
	(mi_field_string, mi_field_fmt): Update.
	(mi_flush, mi_redirect, field_separator): Update.
	(mi_open, mi_close): Update.
	(mi_out_buffered, mi_out_rewind, mi_out_put): Update.
	(mi_out_data_ctor, mi_out_data_dtor): New functions.
	(mi_out_new): Call mi_out_data_ctor.

testsuite/gdb/ChangeLog:

	* lib/gdb.exp (skip_python_tests_prompt): Renamed from
	skip_python_tests.  New arg prompt_regexp.
	(skip_python_tests): New function.
	* lib/mi-support.exp (mi_skip_python_tests): New function.
	* gdb.python/py-mi-objfile-gdb.py: New file.
	* gdb.python/py-mi-objfile.c: New file.
	* gdb.python/py-mi-objfile.exp: New file.