More CSL features: multiple citations and paragraph format

[Omikhleia]

Currently based on #2228 - to rebase accordingly

Objectives

• Properly grouped mutiple citations
• Handling of the CSL indentation rules (hanging-indent, second-field-align) in order to support more styles effectively (stretch goal: with IEEE as main target).
• I think it will then also be the right time to switch to csl mode by default, while still keeping the legacy stuff for now.

Changes

• Some code refactors
• Some fixes and improvements
• \nocite command for marking an entry as cited with out actually citing it (= force its inclusion in the list of cited works, as with LaTeX)
• \cites command for grouped (multiple) citatations

Other notes

On the way, I tested a few more styles, now guaranteed not to crash 🤣 and produce something at least decent 🐰

• IEEE (for the indentation rules) w/ and w/o URL.
• ISO690 (author-date) and ISO690 (numeric), both English and French styles (I was told this one is often used in French papers, so heh)... And there was a bug in our locale logic (fix: Apply default locale on locale overrides without xml:lang). Doh.
• APA, as several French styles are APA-derivatives (... and I thought APA was for Psychology-related journals, but apparently is used in many other contexts, incl. Humanities).
• ACS

Closes #2196

Closes #2023

[Omikhleia]

Stretch goal achieved:

[Omikhleia]

Bonus point achieved:¹

Footnotes

1. Current implementation does not honor display (left-margin, right-inline etc.) but at least doesn't crash and looks "decent" 😹 -- One small thing (highlighted) not investigated yet. ↩

[Omikhleia]

One small thing (highlighted) not investigated yet ... but at least doesn't crash ...

Asouqi's Online Bibtex Converter gets it right:

Interesting, "choose/if" blocks should probably inherit the upper group delimiter:

  <macro name="issue">
    <group delimiter=", ">
      <text variable="volume" prefix="Vol.&#160;"/>
      <choose>
        <if variable="volume">
          <text variable="issue" prefix="no.&#160;"/>
          <text variable="page" prefix="p.&#160;"/>
        </if>
        <else-if variable="issue">
          <text variable="issue" prefix="No.&#160;"/>
          <text variable="page" prefix="p.&#160;"/>
        </else-if>
        <else>
          <text variable="page" prefix="P.&#160;"/>
        </else>
      </choose>
    </group>
  </macro>

I'll see if I can get it on this row of changes, or open a dedicated issue if time runs too short (as I am close to my "max allocated time" for the quarter 😄 )

EDIT: I should write a booklet "SILE and the web of citation styles. A critical assessment" in the same vein as my booklet on maths. This de facto CSL standard is slightly better than MathML (that is, as with so many standards in our doomed world, is quite bad, but at least this is an understandable shit here). 🤣

EDIT2: Aha! CSL "Delimiters from the nearest delimiters from the nearest ancestor delimiting element are applied within the output of cs:choose (i.e., the output of the matching cs:if, cs:else-if, or cs:else; see delimiters)" ... and I had left a FIXME for that exact mention. Now I understand where it's used and why 🤣

[Omikhleia]

• ISO 690 is now good (also with uppercase authors)
• IEEE is better (correct name ordering, and abbreviation of given names)
  For the record the following issue is not ours:
  
  It was introduced in the CSL style between late 2021 (what Asouqi's online translator uses for its predefined toggle) and 2024 (confirmed by using the latest CSL in that same tool; I haven't tried to bissect the commit). This is what happens with too complex standards and no proper regression tests...

[Omikhleia]

• APA looks better too (consistent superscripts across entries).

I think I am done with the things I wanted to see here.