Add chat_log_level setting

[SmallJoker]

Closes #9199.

• New setting chat_log_level to log to the chat
• Colored similar to the terminal output (color codes somewhat trivial, debatable)
• log.h cleanup -> move to source file for compiling time

To do

This PR is Ready for Review.

How to test

1. Heat your room by recompiling the entire Minetest source code
2. minetest.conf:

chat_log_level = info

3. Get spammed.

[SmallJoker]

No functional changes. Added braces here according to the code style guidelines.

[SmallJoker]

Pinging @Wuzzy2 because he requested this feature.

[Wuzzy2]

Thanks, I have tested this for a bit now. So, one problem I found is that Minetest does not guarantee the log message actually appears in chat if that log message appears early at startup time.

I can reliably reproduce this with the following steps:

1. Create a dummy mod with a single line: minetest.log("warning", "THIS IS A TEST WARNING!")
2. Set chat_log_level to warning
3. (Re-)Start Minetest
4. Enable the dummy mod
5. Start Minimal Development Test

The warning should be visible in chat. But it won't be visible. When I restart Minimal Development Test (WITHOUT restarting Minetest!), the warning will then reliably appear on every subsequent restart.
Apparently the log message fails to appear at the startup of game if you started up a game for the first time in the current Minetest session. At least that's how it looks to me. There might something else be going on as well. If you restart Minetest, you will get the same results.

Now some random nitpicks:

Like "Debug log level" but shows log messages in the chat.

Restart Minetest to apply changes.

I don't like descriptions that are written in the form “it works like setting XYZ”. Better write a full standalone description instead, even if it's a little redundant. Why? Because in Minetest, the user will only see one setting description at a time, and it's just inconvenient when you have to hunt down the other setting just to find out what chat_log_level does.

There's a leading space before the tab in line 400 of src/log.cpp.

[SmallJoker]

@Wuzzy2 Thanks for testing. I fixed your reported issues in d8119d5.

[Wuzzy2]

Works fine for me now.

[sfan5]

Works.