Footnote text is duplicated in some cases

Just pulling a small comment on a PR out to an issue so that it does not get lost now that the PR is merged: https://github.com/KhronosGroup/OpenCL-Docs/pull/1018#issuecomment-1841029912

> Related question, the way the footnotes are currently marked up as, more or less 'footnote:[{some attribute containing text}]' resulting in a lot of copies of some footnotes. I believe if they were re-done as '{some attribute containing footnote:label[text]}', each footnote would only appear once, yet would still work when they appear in refpages. I could pick this up in the draft extension integration branch, if you like.

This is particularly obvious in e.g. the [OpenCL C spec](https://registry.khronos.org/OpenCL/specs/3.0-unified/html/OpenCL_C.html#_footnotedef_11).

Assigning to @bashbaug simply because initial question was directed at him.