Porting Riak TS to OTP 26 (it applies to Riak KV also)

[mcesaro]

I successfully compiled Riak on OTP 26.0 based on the riak_ts-3.0.0 branch available at https://github.com/TI-Tokyo/riak/tree/riak_ts-3.0.0
The process involved:

• the update of redbug to the latest version {redbug, {git, "https://github.com/massemanet/redbug", {branch, "master"}}} in therebar.config of the riak_kv project;

• the update of leveled to the latest version (currently the develop-3.1 branch). Note that I wasn't able to build the project using the dependency resolved by rebar3, as the default configuration seems to always checkout a 0.9.*tag of leveled.
  That version won't compile:

leveled_bookie.erl:716:60: type variable 'Key' is only used once (is unbound)

so I had to replace the /src and /include directories with those I got from the forked leveledrepository.

• in riak_core and riak_kv I replaced the dbg:stop_clear/0 calls with dbg:stop/0

-the following type definitions don't compile:

riak_kv_yessir_backend.erl:275:29: type variable 'Index' is only used once (is unbound)
riak_kv_yessir_backend.erl:275:36: type variable 'SecondaryKey' is only used once (is unbound)

riak_kv_eleveldb_backend.erl:182:29: type variable 'Index' is only used once (is unbound)
riak_kv_eleveldb_backend.erl:182:36: type variable 'SecondaryKey' is only used once (is unbound)

the fix is trivial, I just prepended an underscore to the variable names.

• last edit was just to fix the following:

http_uri:decode/1 is deprecated and will be removed in OTP 27; use uri_string:unquote function instead

I fixed the deprecation warnings because they are handled with macros inside the source code:

-ifdef(OTP_25).
percent_encode(A) ->
    uri_string:quote(A).
-else.
percent_encode(A) ->
    uri_string:unquote(A).
-endif.

The version check fails on OTP 26.