Draft: Improve LaTeX rendering

Fixes #17071. When the string has a positive even number of dollars then it is splitted in pure math and text chunks, in order to render text as upright roman text (taking spaces into account) and math as regular math. LaTex default fonts are used, i.e. Computer Modern family. This gives to Scilab the same feature as Matlab (when text entity interpreter is 'latex'). Note: in the future, an "interpreter" property should be added to text entities, as the automatic selection of a given renderer (none, latex, mathml) is not sustainable. For example, It is actually impossible to display "verbatim" text (not rendered whatever the presence of dollars or <>).