[LyX/master] MathML: update code for InsetMathCases to newest classes.

[Thibaut Cuvelier]

commit 6c22e32cee2eafcf6fed6cbd72478f36f5accd75
Author: Thibaut Cuvelier <tcuvelier at lyx.org>
Date:   Fri Dec 9 01:49:19 2022 +0100

    MathML: update code for InsetMathCases to newest classes.
    
    Based on a commit from lynx <lorenzobertini97 at gmail.com>
    
    Part of bug #12590.
---
 src/mathed/InsetMathCases.cpp |    5 ++---
 1 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/src/mathed/InsetMathCases.cpp b/src/mathed/InsetMathCases.cpp
index 082e956..4332cbf 100644
--- a/src/mathed/InsetMathCases.cpp
+++ b/src/mathed/InsetMathCases.cpp
@@ -141,10 +141,9 @@ void InsetMathCases::maple(MapleStream & os) const
 
 void InsetMathCases::mathmlize(MathMLStream & ms) const
 {
-	ms << "<" << from_ascii(ms.namespacedTag("mo"))
-	   << " form='prefix' fence='true' stretchy='true' symmetric='true'>"
+	ms << MTagInline("mo", "form='prefix' fence='true' stretchy='true' symmetric='true'")
 	   << "{"
-	   << "</" << from_ascii(ms.namespacedTag("mo")) << ">";
+	   << ETagInline("mo");
 	InsetMathGrid::mathmlize(ms);
 }