feat: extract multiple comments per translation ID

[Bertg]

This PR resolves #845

On par file level is collects multiple extractedComments (using the same name as pofile package)
This - just like origins - gets merged together to build the catalogue.

Some refactoring was done to use the extractedComments name throughout.

Possible issues

This change should just work for PO file users.
However if users are using lingui file type thing might break. Namely the description (string) is replaced with extractedComments (string[]). Either some backwards compatibility should be built on top of these changes, or sufficient change information should be provided.

What can be improved*

Currently the PO file gets built like with extractedComments and references grouped:

#. Comment in code
#. Other comment
#: App.js:12
#: Screen.js:56
# msgid "Nice"

It would be cool to output them with comment associated with the reference file.

#: App.js:12
#. Comment in code
#: Screen.js:56
#. Other comment
# msgid "Nice"

However, it seems that PO file here is major blocker and this change would be way to much work to achieve.

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[codecov]

Codecov Report

Merging #854 (835d5a1) into main (fa9546e) will increase coverage by 0.09%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #854      +/-   ##
==========================================
+ Coverage   83.01%   83.11%   +0.09%     
==========================================
  Files          51       51              
  Lines        1419     1421       +2     
  Branches      386      388       +2     
==========================================
+ Hits         1178     1181       +3     
+ Misses        142      140       -2     
- Partials       99      100       +1     

Impacted Files	Coverage Δ
...ackages/babel-plugin-extract-messages/src/index.ts	84.34% <100.00%> (+0.41%)	⬆️
packages/cli/src/api/catalog.ts	82.98% <100.00%> (+0.51%)	⬆️
packages/cli/src/api/formats/po.ts	100.00% <100.00%> (ø)

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[tricoder42]

However if users are using lingui file type thing might break.

Well, lingui format was originally just a json dump of the whole catalog, so we could leave there comments as an array.

[tricoder42]

Looks great! Thank you for working on this! 👍