Add wear bar color API

[techno-sam]

Adds an api for modders to change the appearance of the wear bar on their tools.

Currently, the tool damage bar (called "wear bar" by dev wiki) color cannot be customized by modders, and is listed under hardcoded features. This PR fixes that by adding fields in item def as well as item metadata to change the appearance. (See lua_api.txt for api specifics)
Resolves #13325

Summary

The wear_bar field in item definitions and item meta allows modders to customize the color of wear bars in a variety of ways.

To do

This PR is Ready for Review.

How to test

In the devtest game, grab a few of the pickaxes (5, 10, 50, and 100 use pickaxes are customized) and dig some stone, allowing their wear bars to appear. Note the progression through different colors (as described by the tool description) when the pickaxe takes more damage.
Additionally, there is a pickaxe called "Wear Bar Color Test," that when punched with will use a random color for its wear bar. You can use the /use_tool command to damage the tool a bit in order to allow the wear bar to appear.

Screenshot demonstrating the different color possibilities:

[Wuzzy2]

Nice. I like it when things get un-hardcoded in Minetest. Could be useful for technic tools which use the wear bar for a charge level.

I did not test but I looked at the documentation. I strongly suggest to explicitly explain the purpose of wear_color in the item definition in a single sentence here. This cross-refererencing stuff is confusing and inconvenient.

Suggestions for future PRs:

• Change color of background
• Allow to hide bar entirely

[FossFanatic]

I'd add wear bar shadows to the list as well.

It's a small detail, but it looks very nice.

[phseiff]

I also think that'd be a great feature, since what is critically high wear (which is basically what the red/yellow color of the wear bar is supposed to indicate) can vary greatly based on what gameplay mechanism the item/ item wear bar is used for and what the wear bar is meant to indicate.

For example if the wear bar is used to indicate temperature (e.g. for a thermometer item) then having it get red when it gets low doesn't make a lot of sense, so allowing modders to change wear bar color for an item via metadata would open a lot of possibilities for how mods can use the little bar under an item.

[srifqi]

Please rebase this PR (do not merge branch) to current master branch. It should only consists of your commits (around 5 or 7 in this PR). You can read more here.

[techno-sam]

Thanks for the link! Being not super experienced with git (I tend to just have 1 or 2 branches on personal projects), I didn't think of the fact that if I didn't force push, the history on github would clash with my rebased history, and so I accidentally did a merge I shouldn't have. All fixed now.

[srifqi]

The concept and implementation look good. I have also tested it, but I have not checked its performance. There are some code styles fix needed, though.

[srifqi]

Just a few changes needed. Sorry for my mistakes in the last review.

[techno-sam]

No problem at all, I really appreciate that you're spending time looking at it.

[srifqi]

This PR looks good to me. Further improvements can be added later.

[Zughy]

@techno-sam rebase needed (we forgot to tell you, sorry!)

[techno-sam]

No problem!
I'll rebase tonight when I have time.

[techno-sam]

Done @Zughy

[appgurueu]

Refactored a bit, please review @techno-sam (and @srifqi) to make sure you're still happy with it. Tested, everything works as expected. Thank you very much for the good work!

[grorp]

Another documentation thing: This PR adds "Wear Bar Color" as a separate top-level section in lua_api.md, akin to "Games" or "Nodes". Please move the newly added documentation into an existing top-level section instead (e.g. into "Definition tables").

[techno-sam]

@appgurueu thanks for your refactor. I'm afraid I forgot to clean up after myself when I condensed the API.

[grorp]

Using wear values directly instead of "durability" values would still be more consistent IMO (what do others think?)

However, if we decide to use "durability" values for whatever reason, it would be good to add a definition of "durability" as 1.0 - (wear / 65535) to lua_api.md, since this term isn't used anywhere else.