* dgud/mnesia/sticky-bug/ERL-768/OTP-15979:
  mnesia: Bump protocol version
  mnesia: Introduce sync_asym_trans protocol

Remove unsupported conversions from the old protocols.
This means mnesia on OTP-R18 nodes is no longer able to connect to
OTP-22 mnesia nodes.

Add protocol conversion for old nodes and sync_asym_trans transactions.

Transactions with sticky locks could with async_asym transactions be
committed in the wrong order, since asym transaction are spawned on
the remote nodes.

See ERL-768.

If add_table_copy was called when a node was starting it deadlock
waiting for mnesia_controller, when schema was not merged.

Abort if that is the case.

If an activity function fails with an error, the stacktrace is
dropped in non_transaction function try/catch clause.
This makes debuging of errors inside a transaction really hard.

Transaction activities handle errors and exits differently, non-transaction
activities should do the same.

Adding the stacktrace to the exit reason when translating errors to exits.

- first stab at fixing index_[read|match_object] w plugins
- do not include index plugins at match ops
- add index_plugin_test_suite
- Increase ix plugin test coverage + bug fix

* maint:
  mnesia: Avoid raise in overload reports

Several processes could invoke adjust_log_writes, which
could cause overload reports.

Optimise ext table dumping

OTP-15588

The original algorithm first grouped ops in a commit by ext engine
type via folding over the list with orddict:append/3, that resulted in
an O(n^2) algorithm.

However, grouping the ops is not needed, the ops can be dispatched to
insert_op/6 one-by-one, after looking up the storage semantics of
their respective engine. This is a much cheaper algorithm, assuming
looking up the storage semantics is cheap (which should be).