fix(designer-ui): Prevent expressions using &...; syntax disappearing from HTML editor

[ek68794998]

• Please check if the PR fulfills these requirements

• The commit message follows our guidelines
• Tests for the changes have been added (for bug fixes/features)
• Docs have been added / updated (for bug fixes / features)

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

Bug fix

• What is the current behavior? (You can also link to an open issue here)

When entering into the HTML editor an expression that contains an HTML entity such as <, it will disappear from the editor upon save or after switching nodes. Fixes #3741.

• What is the new behavior (if this is a feature change)?

Expression no longer disappears.

• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)

No

• Please Include Screenshots or Videos of the intended change:

Showing token not disappearing:

When the above example is saved, it properly serializes when being sent to the server:

AB#25970447

[ek68794998]

Dropping back to a draft while I work on fixing test case (see comments). Fixed; see resolved comment.