Equation Structure Content Unexpectedly in Text Mode When Created While in LaTeX Linear Mode

eDAD tracking ticket for this issue is [Accessibility 228597](https://dev.azure.com/CSS-IRT/CSS%20IRT/_workitems/edit/228597)

## Description:
If the current equation input mode to "LaTeX Input" in the Conversions group on the Equation ribbon, then input typed into a structure's content holders behaves as if it is in "Text Mode" instead of "Math Mode".

## Steps to Reproduce:
1. Open Microsoft Word 365 (Desktop version).
2. Create a new document.
3. Set the default document language to "English (United States)"
4. Press "Alt+=" to bring up the equation editor
5. In the "Conversions" group on the "Equation" ribbon, select "LaTeX" input.
6. In the "Structures" group, select "Fraction", and then "Stacked Fraction"
7. Navigate to the numerator's placeholder and type "a+b"
8. Navigate to the denominator's placeholder and type "1-5"
9. Navigate to the right to leave the stacked fraction and then press "Enter" to leave the expression.
10. Note that the variables 'a' and 'b' are not converted into the "math font" and the "1-5" is not converted into math (no spacing is placed around the '-' character and the size of the '-' character is unchanged.
11. Use the Read Aloud feature to read the expression.
12. Note that the 'a' is spoken with the soft 'a' sound instead of the long 'a' sound. Also note that the denominator is read aloud as "One to five" instead of "One minus five".
13. Move the input cursor into the expression and attempt to convert the expression into the "Professional" form one or more times. Note that the expression remains unchanged.

## Expected Behavior:
When in "LaTeX" input mode, content placed into a structure's content placeholders should behave the same as it does when not in a structure's content place holder.

## Version Information:
- **OS Version:**
-- OS Name: Microsoft Windows 11 Enterprise
-- Version: 10.0.22631 Build 22621
-- Locale: United States
- **Microsoft Word Version:**
-- Microsoft® Word for Microsoft 365 MSO
-- Version 2402 Build 16.0.17328.20346 64-bit

## Video Demonstration
[Video: Equation Structure Placeholder Content Unexpectedly in Text Mode When Created While in LaTeX Linear Mode (4 minutes)](https://iu.mediaspace.kaltura.com/media/t/1_1rj35etl)