Add missing FVector2/3/4 methods to Vector classes

**Issue by [error454](https://github.com/error454)**
_Wednesday Jul 03, 2019 at 02:40 GMT_
_Originally opened as https://github.com/SkookumScript/SkookumScript-Plugin/issues/4_

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**Is your feature request related to a problem? Please describe.**
When you do a lot of vector work in C++, you get used to using certain helpers and methods on the vector types. Functions like `GetUnitAxis` for example, which aren't even exposed to BP but are invaluable.

**Describe the solution you'd like**
It would be great to have feature parity between the C++ `FVector` types and the sk `Vector` types.

**Additional context**
This may be brute-force manual additions to the `Vector2/3/4` classes, see [Vector2 impl](https://github.com/SkookumScript/SkookumScript-Plugin/blob/005abdae66d1a591092414a6f7d1a2880f387bb9/Source/SkookumScriptRuntime/Public/Bindings/VectorMath/SkVector2.hpp). But it sure would be nice if we could scrape and auto-generate bindings with some meta-programming and then set it loose on the entire FMath library. Unfortunately, many of the math methods do not have `UFUNCTION` macros so using UHT isn't an option.

Source/SkookumScriptRuntime/Public/Bindings/VectorMath/SkVector2.hpp から始め、既存の SkookumScript の Vector2、Vector3、Vector4 バインディングを C++ の FVector API と比較します。不足しているメソッドを特定し、手動で追加する方法と生成されたバインディングのどちらがプロジェクトの制約に適合するかを判断します。要求されたベクトルヘルパーが、サポートされている C++ メソッドと機能面で同等になれば完了です。

索引モデルが issue の本文から書いたものです。