[pdata] Add Append and EnsureCapacity methods to primitive slices

[dmitryax]

Follow-up PR from #5971:

No way of increasing the capacity or length. We can discuss about that API.

Given that we have SetAt interface not Append..., I think it makes sense to have SetLen. But I'm open to other suggestions

Fixes #6063

cc @bogdandrutu

[codecov]

Codecov Report

Base: 91.58% // Head: 91.60% // Increases project coverage by +0.01% 🎉

Coverage data is based on head (f098fc3) compared to base (4cf5f82).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6060      +/-   ##
==========================================
+ Coverage   91.58%   91.60%   +0.01%     
==========================================
  Files         217      217              
  Lines       13424    13454      +30     
==========================================
+ Hits        12295    12325      +30     
  Misses        906      906              
  Partials      223      223              

Impacted Files	Coverage Δ
pdata/pcommon/generated_primitive_slice.go	100.00% <100.00%> (ø)

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[bogdandrutu]

Given that we have SetAt interface not Append..., I think it makes sense to have SetLen. But I'm open to other suggestions

Confused about why not offering an Append(vals ...int64) is not a valid solution as well?

Some other question:

1. Should we also offer EnsureCapacity?

[dmitryax]

@bogdandrutu My reasoning for SetLen is coming from the usage. Usually we know length in advance and just set/update existing elements not appending anything.

Maybe we shouldn't rely on usage and think of the slices in more abstracted way. In that case Append and EnsureCapacity probably is better, since it provides more flexibility going forward. The only downside is that there is no way to shrink the slice without extra allocation. Not sure if it's really feasible use case

[bogdandrutu]

I think an Append and EnsureCapacity make total sense and moves this so be similar with other slices. In addition we can also have SetLen but want tot understand if it does allocation if not enough space or crash (for example reslicing a slice crash if not enough capacity). I think SetLen can wait until we see more use-cases, what do you think?

[dmitryax]

I think SetLen can wait until we see more use-cases, what do you think?

Ok sounds good. let's do that

[dmitryax]

@bogdandrutu , updated

[bogdandrutu]

Need a rebase

[dmitryax]

Rebased