FR: Add lerp math function

Something like this, but probably with more of that safety stuff:

    // Somewhere in "modules/juce_core/maths/juce_MathsFunctions.h":

    /** */
    template<typename Type>
    constexpr Type lerp (Type a, Type b, Type t)  { return a + (t * (b - a)); }

Isn’t that exactly what juce::jmap (t, a, b) does?

Oh ffs… Totally forgot about that rendition of jmap. Thanks!

Edit: I guess this post can be deleted…