frametitlecaps option causes footnotes in title to be printed in all-caps

[michaelroland]

Issue

When the frametitlecaps option is enabled, footnotes in frametitles get shown in all-capital letters.

Steps to reproduce

\begin{frame}
\frametitle{My Frame\footnote{This slide is very important!}}
\begin{itemize}
\item Item 1
\item Item 2
\item Item 3
\end{itemize}
\end{frame}

Expected behavior

Footnote should not be \MakeUppercase'd.

[michaelroland]

Looking at https://tex.stackexchange.com/a/374633/290236, it might just be wrong to use \footnote in the title. We may need to use \footnotemark (in combination with \footnotetext outside the title) instead.

See https://tex.stackexchange.com/a/474450/290236 for a potential solution. Can we re-define \footnote inside frametitle to do exactly this?