angle-bisector-theorem: replace numeric with symbolic angle

Due to rounding errors when converting to niceAngles,
the numeric value displayed can lead to invalid
triangles. i.e. an SSA triangle with side, side, angle
values that produces a triangle that does not exist.

This change is to just replace the numeric rounded value
displayed with a theta character to show that the angles
are equal and that the bisector theorem can be used.