Move data type of axes limits and mouse plot pos from float to double

[SamuMazzi]

Description:
Lately this topic has been discussed more than usual (like here) so I decided to make public what I've done some time ago. It's a simple and probably naive solution, so I'm open to improvements.

This solution actually closes #1847 (I've tested the example) and hopefully it should close #2067, #386 but on the other side I think it's still not enough precision for this #2157

Concerning areas:
I've also read that @v-ein has (rightly) made the point of performance, but it shouldn't really be a problem (as far as I read, both from @axeldavy and the internet) also because double type has been already used in a while by ImPlot.

Notes:
I've also changed the data structures from ImVec2 to ImPlotRange, I hope it's not a problem.

[khazaddim]

I would really love to see this implemented. I want to be able to get the position of my mouse in time on a candlestick chart with minute resolution (or with this change second as well I think!!)

[khazaddim]

Hey, just checking in on this. I'm working on other parts of my project while I wait on this.

[v-ein]

Bad news: this (and all other PRs) will go after #2282, which is my main target for now (just don't want to context switch even more than now). I've been away from DPG for a while due to lack of free time - hence the slow progress; planning to spend more time on PRs starting in a couple of weeks.