#4699 displa, tex and lurkmathml display of partial derivatives is incorrect

[Leo Butler]

Consider:

$ ./maxima-local --no-init
Maxima branch_5_49_base_188_g2bd018694 https://maxima.sourceforge.io
using Lisp SBCL 2.6.0.debian
Distributed under the GNU Public License. See the file COPYING.
Dedicated to the memory of William Schelter.
The function bug_report() provides bug reporting information.
(%i1) [f,g]:[x*y+%e, x^2*%e]$

(%i2) ['diff(f,x),'diff(g,x)];
                           d              d       2
(%o2)                     [── (x y + %e), ── (%e x )]
                           dx             dx
(%i3) map(tex,%o2);
$${{d}\over{d\,x}}\,\left(x\,y+e\right)$$
$${{d}\over{d\,x}}\,\left(e\,x^2\right)$$
(%o3)                           [false, false]
(%i4) load(mathml)$
(%i5) map(mathml,%o2);
 <math xmlns="http://www.w3.org/1998/Math/MathML"> <mfrac><mrow>
 <mtext>&DifferentialD;</mtext></mrow> <mrow><mtext>&DifferentialD;</mtext>
 <mspace width="0.16666667em"/><mi>x</mi> </mrow></mfrac> 
 <mspace width="0.16666667em"/><mrow><mo>(</mo><mi>x</mi> 
 <mspace width="0.16666667em"/><mi>y</mi> <mo>+</mo> <mi>&ExponentialE;</mi> 
 <mo>)</mo></mrow> </math>
<math xmlns="http://www.w3.org/1998/Math/MathML"> 
 <mfrac><mrow><mtext>&DifferentialD;</mtext></mrow> <mrow>
 <mtext>&DifferentialD;</mtext><mspace width="0.16666667em"/><mi>x</mi> 
 </mrow></mfrac> <mspace width="0.16666667em"/><mrow><mo>(</mo>
 <mi>&ExponentialE;</mi> <mspace width="0.16666667em"/><msup><mrow><mi>x</mi> 
 </mrow> <mn>2</mn> </msup> <mo>)</mo></mrow> </math>
(%o5)                           [false, false]

I would expec that 'diff(f,x) is typeset as a partial derivative (but it is not in either of the three cases), while diff(g,x) is an ordinary derivative. There is a secondary issue, too, in that the &Differential; operator is enclosed in an mtext element; it should be mo.