Improve availability filter

[Hlavtox]

Questions	Answers
Description?	Several small improvemets to availability filters. Details below.
Type?	improvement
BC breaks?	no
Deprecations?	no
Fixed ticket?	Doesn't fix an issue, but will fix about thousand complains from merchants.
How to test?	Check that stock filter works correctly.

Changes

• Many people complain that they have three values - "Not available", "Available" and "In stock". Now, if the products Available and In stock are the same, it will don't display "Available".
• I removed automatic sorting by language for availability. Now they will be fixed in this order - "In stock", "Available", "Not available".
• Even if "In stock" is the last option with products, it will still be displayed, so people know if the X products remaining are in stock or not. Not everybody has stock displayed in their product list.

How it looks - nicely ordered, if there is something orderable but not in stock, it is still displayed

But when they are the same 7 products, or merchant does not allow out-of-stock ordering globally, it won't get displayed

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This change is 

[matthieu-rolland]

just some uneducated feedback... and also I'm wondering if this should be validated by @MatShir before being QAed and merged

[matthieu-rolland]

Seems like product aproves (@MatShir ) 👍

LGTM codewise

[AureRita]

Hi @Hlavtox

Thank you for your PR, All seems to works as you can see here :

Untitled_.Jul.24.2023.5_03.PM.webm

Tested on :
1.7.8.10 ✔️
8.1.1 ✔️
8.0.5 ✔️

I see just a little issue on it :
If you've already load the previous faceted search, when you update, if you don't the state of any product, the faceted search'll continue to be like before, only in your languages, as you can see :

Untitled_.Jul.24.2023.5_31.PM.webm

I don't think this one'll block this PR so it's QA ✔️

Thank you

[Hlavtox]

Thanks @AureRita, I will flush the cache on upgrade. ;-) #884

[MatShir]

🥳