Also add static identifier as upstream did

always evaluate to true.

This was needed due to the TileDef serialisation changes. Originally it has been planned
to also add utf-8 based chat to 26, but chat changes aren't final yet, so they are done
in one change, after the release, and not two small ones, causing us having to be compliant
to three versions of the packet.

Enable the server to request the client to reconnect.

This can be done with the now extended minetest.request_shutdown([reason], [reconnect]) setting.

Tune and optimise noise parameters

-> Fix server crash with protocol >=25 if a default password is set.
-> Remove some useless and possibly confusion causing code for the TOCLIENT_FIRST_SRP packet handler

-> Fix bug where MoveSomewhere from an infinite source would fill the destination inventory with copies of itself.
-> Fix bug where MoveSomewhere would needlessly call callbacks.
-> Remove trailing whitespaces

Mgv5/mgv7: Remove 'should make cave hole' feature
Remove ravine code

Replaces while loops with proper getfield calls

The doc and the actual behaviour differed.

Also don't show "probably running a different version" message in simple singleplayer mode

Improve TOCLIENT_ACTIVE_OBJECT_MESSAGES robustness for handling invalid data

Add serializeHexString()
Clean up util/serialize.cpp

Spare some copies.

The neighbours checked are the 8 nodes horizontally surrounding the decoration base
and the 8 nodes horizontally surrounding the ground node below the decoration

Use wide_to_utf8 and utf8_to_wide instead of wide_to_narrow and narrow_to_wide at almost all places.
Only exceptions: test functions for narrow conversion, and chat, which is done in a separate commit.

- Fixed race conditions
- Fixed null dereference
- Fixed out-of-bounds array access
- MinimapMapblock is now allocated and added to update queue only when enabled
- Removed dependency on LocalPlayer
- Fixed code style
- Simplified expressions and program logic
- Cleaned minimap object interfaces

Lowest level of base terrain determines mountain generation in mapchunk
Change some positional function arguments from int to s16

Previously, m_proto_ver was set to the serialisation version
inside the legacy init packet.

Now, if the server doesn't send a protocol version (protocols < 25),
we set m_proto_ver to some value < 25 and > 0.