Simplify sorting and make it more readable

[S-S-X]

Main changes:

• Overall LoC +105 −165 (which already includes few unrelated additions)
• Makes filtering safe (deliberate invalid Lua pattern to crash server)
• Makes filtering and sorting happen on demand, wont filter or sort if results wont be actually used.
• Makes sorting function more readable and utilizes in place sorting.

Be aware that this is incomplete work.
There's 2 operation modes for sortfield == "1", this is because I was not sure how exactly it is supposed to work. Fixed.
Maybe it is supposed to be like a.from < b.from or a.to < b.to ? Fixed.

This will also modify original table but I think that shouldn't be problem, not 100% sure though... Checked this too, now makes shallow copy.

[Athozus]

Be aware that this is incomplete work.

There's 2 operation modes for sortfield == "1", this is because I was not sure how exactly it is supposed to work.

Maybe it is supposed to be like a.from < b.from or a.to < b.to ?

This will also modify original table but I think that shouldn't be problem, not 100% sure though...

Okay, when I tried it worked very well. Maybe you will find issues, but the problem is that I wouldn't create a global function storing sorting data, and as this is a table of messages containing tables with info, it's hard to reproduce a table.sort-like function.

[Athozus]

Totally good, thx !

[S-S-X]

I've converted this back to draft because it still does not implement all functionality, we discussed this in mt-mods discord and results can be found from another PR which targets this branch.

• Rework mail.sort_messages #59

So before merging this one either #59 should be merged and tested or missing functionality added directly to mail.sort_messages.

My personal preference, go with #59 instead of reinforcing formspec/ui dependency on mail.sort_messages.

[Athozus]

Very good work, for me it's doesn't present anything weird. I approve the merge.

No issues found.