Make index array more similar to unbundle cluster

[jkirschner]

Index Array FPGA documentation: Resources - This function consumes logic resources in proportion to the size of the array.

Unbundle by Name FPGA documentation: Resources - The Cluster & Class functions consume no logic resources on the FPGA because they are purely wiring operations.

Though this is not a major issue, it would decrease resource usage proportional to the size of array the user is dealing with if these behaved similarly.

[Dragis]

Good catch! The documentation is actually a bit ambiguous. If the index going into the Index Array node is not a constant, then the documentation is correct, you get a large mux that allows you to select any element at runtime. However, if the index is a constant value, the compiler will optimize out the mux and it is equivalent to the Unbundle by Name. 

[Dragis]

An internal request to fix the documentation has been created.