feat(collections): add index arg to methods

[canac]

Adds an index arg to collections' predicate/selector/transformer/discriminator method. I added it only to collection helpers that operate on iterables because collection helpers that operate on records don't seem as likely to need access to the key index. Please let me know if I missed any.

Closes #6288

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.17%. Comparing base (8df6974) to head (c0c394e).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6382   +/-   ##
=======================================
  Coverage   94.16%   94.17%           
=======================================
  Files         592      592           
  Lines       42975    42990   +15     
  Branches     6807     6807           
=======================================
+ Hits        40466    40484   +18     
+ Misses       2458     2456    -2     
+ Partials       51       50    -1     

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[kt3k]

I'm generally in favor of the idea. It looks useful in several places, and also this is aligned to the design of builtin map methods (such as map, filter, forEach, etc)

What do people think?

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Note: Currently we have policy of accepting any new feature in unstable_ prefixed path. That requires all these APIs duplicated in unstable_foo.ts, but that feels too unwieldy in this case. I'll discuss with core team about how to handle this particular case.

[timreichen]

What do people think?

I like it.

[iuioiua]

I'm in favour.

[iuioiua]

@kt3k should we add this in?

[canac]

I'm more than happy to rebase this if we want to move forward with it. Just let me know!

[iuioiua]

I suggest rebasing anyway 🙂