Support for Text with Null Material/DisplayStyle

[AlexandruPopovici]

Description & motivation

The viewer now supports text with no specified material/display style by defining it's own default text null material, similarly to how all the rest of the object types have

Changes:

• Materials now defines it's null text material hash + material
• TextBatch now properly computes it's bounds

To-do before merge:

Screenshots:

Validation of changes:

Checklist:

• My pull request follows the guidelines in the Contributing guide?
• My pull request does not duplicate any other open Pull Requests for the same update/change?
• My commits are related to the pull request and do not amend unrelated code or documentation.
• My code follows a similar style to existing code.
• I have added appropriate tests.
• I have updated or added relevant documentation.

References