Option for parentheses around equation numbers reference in addition to `eq-prefix`

[cderv]

Discussed in #2413

^{Originally posted by jordan-melendez September 12, 2022}
In certain journals it is common to format references to equations like Eq. (1.1) with parentheses around the equation number. Quarto supports modifying Eq. with eq-prefix, but would it be possible to either

1. Add a parameter similar to eq-prefix that allows one to customize the reference further, and/or
2. Ensure that, when compiled to PDF, \eqref gets used rather than \ref for equation references. This would require amsmath I suppose, but would automatically add parentheses and permit further customization.

Thanks!

[cderv]

Some notes:

\eqref is defined in amsmath, and seems widely use for referencing equation as it adds the parenthesis (https://en.wikibooks.org/wiki/LaTeX/Labels_and_Cross-referencing#eqref). Maybe we could add an option so that \ref can be replaced by \eqref for equations ?

quarto-cli/src/resources/filters/crossref/refs.lua

Lines 68 to 70 in c16212c

	-- for latex inject a \ref, otherwise format manually
	if _quarto.format.isLatexOutput() then
	ref:extend({pandoc.RawInline('latex', '\\ref{' .. label .. '}')})

This would be for LaTeX output only, possibly useful in Quarto Journals - Allowing to tweak that through a Lua filter could also be a way to solves this for PDF only.

More generally, support parenthesis around reference for equation in HTML and PDF requires some specific formatting work for HTML outputs.

[cscheid]

Re-milestoning it to match the rest of our crossref work (even if we eventually choose to move it to 1.3, this seems like a natural thing for us to support)