fix(animations): Add missing \pgf@sys@tonumber before <dimen>

"Private" implementations of `pgfmath` functions only accept unit-less
numbers as their arguments, e.g.,
    \pgfmathadd@{1.0}{1.0}
So every dimension used as their argument must be prefixed by a `\pgf@sys@tonumber`, e.g.,
    \pgfmathadd@{\pgf@sys@tonumber\pgf@x}{\pgf@sys@tonumber\pgf@y}

This eliminates "Missing character" reports for `p` and `t`.

Signed-off-by: muzimuzhi <muzimuzhi@gmail.com>

tex/generic/pgf/systemlayer/pgfsysanimations.code.tex

@@ -890,7 +890,7 @@
       % Interval too small: Goto end of interval
       \def\pgfmathresult{1.0}%
     \else%
-      \pgfmathdivide@{\pgf@ya}{\pgf@xa}%
+      \pgfmathdivide@{\pgf@sys@tonumber\pgf@ya}{\pgf@sys@tonumber\pgf@xa}%
     \fi%
     \pgf@x\pgfmathresult pt\relax%
     \expandafter\pgfsysanim@splitter\the\pgf@x%
@@ -926,7 +926,7 @@
     % Interval too small: Goto end of interval
     \def\pgfmathresult{1.0}%
   \else%
-    \pgfmathdivide@{\pgf@ya}{\pgf@xa}%
+    \pgfmathdivide@{\pgf@sys@tonumber\pgf@ya}{\pgf@sys@tonumber\pgf@xa}%
   \fi%
   \pgf@x\pgfmathresult pt\relax%
   \expandafter\pgfsysanim@splitter\the\pgf@x%
@@ -971,7 +971,7 @@
       % Interval too small: Goto end of interval
       \def\pgfmathresult{1.0}%
     \else%
-      \pgfmathdivide@{\pgf@ya}{\pgf@xa}%
+      \pgfmathdivide@{\pgf@sys@tonumber\pgf@ya}{\pgf@sys@tonumber\pgf@xa}%
     \fi%
     \pgf@x\pgfmathresult pt\relax%
     \expandafter\pgfsysanim@splitter\the\pgf@x%
@@ -1001,7 +1001,8 @@
     % Interval too small: Goto end of interval
     \def\pgfmathresult{1.0}%
   \else%
-    \pgfmathdivide@{\pgfsysanim@snap@repeat@arg}{\pgf@xa}%
+    % `\pgfsysanim@snap@repeat@arg` is a macro storing a dimen value, eg "4.0pt"
+    \pgfmathdivide@{\pgf@sys@tonumber\dimexpr\pgfsysanim@snap@repeat@arg}{\pgf@sys@tonumber\pgf@xa}%
   \fi%
   \pgf@x\pgfmathresult pt\relax%
   \expandafter\pgfsysanim@splitter\the\pgf@x%
@@ -1823,7 +1824,7 @@
       \def\pgfsysanim@frac@b{1}%
     \else%
       \let\pgfsysanim@divby\pgfmathresult%
-      \pgfmathsubtract@{\pgf@xc}{\pgfsysanim@prev@time}%
+      \pgfmathsubtract@{\pgf@sys@tonumber\pgf@xc}{\pgfsysanim@prev@time}%
       \pgfmathdivide@{\pgfmathresult}{\pgfsysanim@divby}%
       \ifdim\pgfmathresult pt<0pt\def\pgfmathresult{0}\fi%
       \ifdim\pgfmathresult pt>1pt\def\pgfmathresult{1}\fi%
@@ -1875,7 +1876,7 @@
       \pgf@ya\pgfsysanim@ft%
       \advance\pgf@ya by-\pgfsysanim@frac@a pt%
       \pgf@yb\pgf@x
-      \pgfmathreciprocal@{\pgf@yb}%
+      \pgfmathreciprocal@{\pgf@sys@tonumber\pgf@yb}%
       \ifdim\pgfmathresult pt>2.5pt%
         \def\pgfmathresult{2.5}%
       \fi%
@@ -1906,7 +1907,7 @@
       \pgf@ya\pgfsysanim@ft%
       \advance\pgf@ya by-\pgfsysanim@frac@a pt%
       \pgf@yb\pgf@x
-      \pgfmathreciprocal@{\pgf@yb}%
+      \pgfmathreciprocal@{\pgf@sys@tonumber\pgf@yb}%
       \ifdim\pgfmathresult pt>2.5pt%
         \def\pgfmathresult{2.5}%
       \fi%
@@ -1938,7 +1939,7 @@
       \pgf@ya\pgfsysanim@ft%
       \advance\pgf@ya by-\pgfsysanim@frac@a pt%
       \pgf@yb\pgf@x
-      \pgfmathreciprocal@{\pgf@yb}%
+      \pgfmathreciprocal@{\pgf@sys@tonumber\pgf@yb}%
       \ifdim\pgfmathresult pt>2.5pt%
         \def\pgfmathresult{2.5}%
       \fi%