footnotes in tex-math

[pkra]

To document what we've been doing:

• footnotes inside tex-math are ok in the XML
• jats-to-html https://github.com/AmerMathSoc/jats-to-htmlbook/issues/200
  • moves footnote content outside of the data-jats=math container
  • rewrites link to foonote inside tex-math to suitable TeX (i.e., makes it superscript - cf. #19)
• ams-html leaves the footnotelink alone, creates a wrapper around the footnote content for hiding/revealing mechanics

[pkra]

Curious side effect: https://github.com/AmerMathSoc/ams-doc-sources/issues/1283

[pkra]

Documented via https://github.com/AmerMathSoc/ams-platform-documentation/commit/34f0c45f2e9d26a76c9c5d8f88c579f57fb7fd0a