Fix markup of product-type constructor call in [exec.just]

[lewissbaker]

The \exposid{product-type} needed some extra @ symbols surrounding so that the subsequent curly-braces for the constructor call are treated as literal text.

[jensmaurer]

No, we need backslashes before the braces.

[lewissbaker]

No, we need backslashes before the braces.

I was copying the syntax used in other places:

• draft/source/exec.tex

  Line 1744 in c8f87ef

  return @\exposid{product-type}@{connect(

• draft/source/exec.tex

  Line 3143 in c8f87ef

  @\exposid{make-sender}@(on, @\exposid{product-type}@{sch, closure}, sndr))

• draft/source/exec.tex

  Line 3587 in c8f87ef

  transform_sender(@\exposid{get-domain-early}@(sndr), @\exposid{make-sender}@(bulk, @\exposid{product-type}@{shape, f}, sndr))

Which seem to be rendering fine on https://eel.is/c++draft/

• https://eel.is/c++draft/exec#snd.expos-29
• https://eel.is/c++draft/exec#on-4
• https://eel.is/c++draft/exec#bulk-2

Do they also need to be changed to escape the braces with backslashes?

[frederick-vs-ja]

I was copying the syntax used in other places:

There are in either \begin{itemdecl} \end{itemdecl} or \begin{codeblock} \end{codeblock}, so the syntax is slightly different. I don't think we need to escape the braces with backslashes in such blocks.

Note that existing occurences of {} in \tcode{} (and outside of blocks) are escaped with backslashes:

draft/source/algorithms.tex

Lines 7166 to 7167 in c8f87ef

	Let \tcode{comp} be \tcode{less\{\}}
	and \tcode{proj} be \tcode{identity\{\}}

[jensmaurer]

Ok, that looks good now.

In order to streamline future instances of the process, please consider https://github.com/cplusplus/draft/wiki/Commit-message-format and squash and force-push your commits (there should be a single commit remaining in this pull request, with a proper one-line change description, after this endeavor).