--[BE Week] Better Attributes Handle search efficiency; Viewer.cpp/Viewer.py text render fixes

[jturner65]

Motivation and Context

This PR leverages the recent updates to our Magnum libs to address some inefficiencies and bugs, and fixes a minor bug with how scene instances were being loaded.

Viewer.cpp/Viewer.py :

1. Improve text rendering in the viewers by using the magnum's new glyph handling.
2. Fix the black-box background around text in viewer.py by enabling, defining and subsequently disabling the appropriate blend state when text is being drawn.

Attributes

1. Speed up string handle match search by checking size of target string before forcing it to lowercase
2. Add missing Articulated Object Attributes verification on Scene Instance load to be consistent with Stage, Object and Lighting Attributes handling.

How Has This Been Tested

Locally all tests pass

Types of changes

• Docs change / refactoring / dependency upgrade
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have completed my CLA (see CONTRIBUTING)
• I have added tests to cover my changes.
• All new and existing tests passed.

[0mdc]

LGTM!

[0mdc]

We probably want to remove this line.