Make it possible to post closures to BTA message queue

Currently, every task executed on bta thread needs a separate event id,
structure holding its parameters, API method, and method that will be
executed in bta thread, which must accept generic tBTA_DM_MSG.

Because of that we end up with lots of boilerplate code, and possibility
to misinterpret bytes in tBTA_DM_MSG struct.

After this patch, we can post closures onto bta thread. Thanks to it we
don't need a struct to hold parameters, and the executed method can have
a meaningful parameters.

First experiments showed over 50% reduction in code size when rewriting
advertising code to new style, not to mention much better readability.

Bug: 30622771
Change-Id: I400839b920c04c67c893899969d07a02d9c1b2e6