[Course Settings] Use Display Name in all Name fields

Problem statement:

When a student has a Display Name, other students in their class can't see their "real" name (legal name) except if the People tab is enabled. While the legal name still show up in these areas of Teacher role: Gradebooks , and SpeedGrader (a pop up window show the Real name) According to our faculty, it's very confusing for them

Proposed solution:

Canvas should use the Display name for all the name fields such as Full Name and Sortable Name to avoid the confusions for faculty and without disabling the People tab too.

User role(s):

admin,designer