feat: msgctxt support

[nakkamarra]

As described as part of: #856

My decision here was to use context / msgctxt as a way to "sub-key" a given key, which I feel lines up more with the original gettext implmentation/intention of context. So if we had a catalog like so:

{
    "keyA": "translationA",
    "keyB": "translationB",
}

the addition of context could be modeled like so:

{
    "keyA": "translationA",
    "keyB": "translationB",
    "contextA": {
         "keyA": "translationAA",
         "keyB": "translationAB"
     },
     "contextB": {
         "keyA": "translationBA"
     }
}

where a given context string acts as the key of another sub-catalog of translations. This allows one to add multiple translations for a given ID / string by using different contexts. To pull out translations, one would reference this.messages[context][id] instead of this.messages[id] in the case that context was defined for a given ID.

On top of that, I think this is actually pretty trivial to support for many of lingui's current formats (po, po-gettext, minimal, and raw), since we're just creating sub-objects and serializing / deserializing them. As far as CSV is concerned, I think there'd need to be a bit of extra work, but it could be possible to apply something similar to what we're doing with JSON (imagine instead of each row being key, translation you have context, key, translation and work with that)

There's the caveat that this does not abstract msgids and solve the shrinking of IDs in catalogs, one of the upsides to @Bertg's approach to this problem.

I'd say this is about 90% of the way there, but I'd love to get some feedback and thoughts around this approach, particularly around this chunk which could be refactored to be much cleaner: https://github.com/lingui/js-lingui/compare/main...nakkamarra:msgctx-support?expand=1#diff-9317c05f72203559bc3788fb80d76d19f38b457e50c35c430463d964574eec90R27-R80

@semoal @tricoder42 @Bertg

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[codecov]

Codecov Report

Merging #1094 (fbdd6a0) into main (54d6b6e) will decrease coverage by 0.38%.
The diff coverage is 70.66%.

@@            Coverage Diff             @@
##             main    #1094      +/-   ##
==========================================
- Coverage   81.88%   81.49%   -0.39%     
==========================================
  Files          56       56              
  Lines        1678     1724      +46     
  Branches      458      474      +16     
==========================================
+ Hits         1374     1405      +31     
- Misses        182      189       +7     
- Partials      122      130       +8     

Impacted Files	Coverage Δ
packages/cli/src/api/catalog.ts	81.48% <ø> (-0.09%)	⬇️
packages/react/src/Trans.tsx	78.57% <ø> (ø)
packages/cli/src/api/formats/po-gettext.ts	82.40% <33.33%> (-1.21%)	⬇️
packages/cli/src/api/formats/po.ts	95.74% <33.33%> (-4.26%)	⬇️
packages/cli/src/api/compile.ts	87.93% <61.53%> (-8.07%)	⬇️
packages/core/src/i18n.ts	71.42% <66.66%> (-4.02%)	⬇️
...ackages/babel-plugin-extract-messages/src/index.ts	79.05% <76.31%> (-3.35%)	⬇️
packages/macro/src/constants.ts	100.00% <100.00%> (ø)
packages/macro/src/macroJsx.ts	91.17% <100.00%> (+0.19%)	⬆️
... and 1 more

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[nakkamarra]

Hey @semoal think you could take a look when you have the chance?

[jeroenvisser101]

@nakkamarra this looks great! @semoal is this something that could make it in a future release? We have a few strings in our application that we have issues with and our current workaround (custom msgids) isn't the greatest way to handle this. Let me know if we can help :)

[nakkamarra]

@jeroenvisser101 thanks, I'm no longer working with lingui and this PR is probably a bit outdated now, but if you wanted to grab this branch and merge the main branch and see if there are any conflicts / changes that need to be made I think it'd be a good way to see this feature make it over the finish line.

[semoal]

It's cool @nakkamarra I reviewed it and look fine to me, let's release a new version tomorrow with this feature and if @jeroenvisser101 finds some issues feel free to open an issue and I'll solve them asap :)

[semoal]

After so much time, finally this is released guys.. Sorry for the delay I've been lately so busy ..
3.13.0