linalg: return out array for .toArray, create symmetric mat3

src/mol-math/linear-algebra/3d/mat3.ts

src/mol-math/linear-algebra/3d/mat4.ts

src/mol-math/linear-algebra/3d/quat.ts

src/mol-math/linear-algebra/3d/vec2.ts

src/mol-math/linear-algebra/3d/vec3.ts

src/mol-math/linear-algebra/3d/vec4.ts