plugins: extend API to get latest memory value accessed

plugins: extend API to get latest memory value accessed

This value can be accessed only during a memory callback, using
new qemu_plugin_mem_get_value function.

Returned value can be extended when QEMU will support accesses wider
than 128 bits.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1719
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2152
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Xingtao Yao <yaoxt.fnst@fujitsu.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Message-Id: <20240724194708.1843704-3-pierrick.bouvier@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20240916085400.1046925-6-alex.bennee@linaro.org>