accel/tcg: Extract statistic related code to tcg-stats.c

Statistic code is not specific to system emulation (except
cross-page checks) and can be used to analyze user-mode binaries.
Extract statistic related code to its own file: tcg-stats.c,
keeping the original LGPL-2.1-or-later license tag.
Note, this code is not yet reachable by user-mode.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20250715140048.84942-3-philmd@linaro.org>