convert Vector2/3/4 methods to standard getter pattern

[pixelzoom]

I took a look at all of the Vector2, Vector3, and Vector4 methods that take zero arguments, i.e. function(). Discussed with @jonathanolson and here are our conclusions.

These were already converted by @samreid and @Denz1994 in https://github.com/phetsims/dot/issues/84:

• magnitude
• angle

These methods are operations that mutate the Vector2 instance. We won't change these.

• normalize
• roundSymmetric
• negate

These methods are operations that return a new instance. There's a well-established naming convention that associates these methods with their mutator versions (e.g. normalize and normalized), and that convention is used throughout dot. So we won't change these.

• normalized
• roundedSymmetric
• negated

So that leaves only 2 methods to convert:

• [x] magnitudeSquared (Vector2, Vector3, Vector4), 32 occurrences of ".magnitudeSquared("
• [x] perpendicular (Vector2), 40 occurrences of ".perpendicular("

[chrisklus]

I'm jumping on perpendicular, @jbphet is on magnitudeSquared.

[jbphet]

The conversions for magnitudeSquared and perpendicular sound now be complete. Marking for dev meeting to decide who is up next.

[samreid]

It appears those were the last two. @jbphet if you concur, this issue can be closed. If I'm wrong, please let me know and re-label for dev meeting.

[pixelzoom]

Yes indeed, those were the last 2 that @jonathanolson and I identified in https://github.com/phetsims/dot/issues/87#issue-413131104. So I'll take the liberty of closing. Feel free to reopen if there's anything I've missed here.