Fix type stability issues for getindex with symbols

[jonniedie]

Constant propagation works for Axis indexing but not for ComponentArray indexing. Not sure what to do here. I’m wrapping the symbolic indexes immediately in a Val and passing them into a function that calls a @generated function. fastindices is a workaround that I’d rather not have to have.

[jonniedie]

Linked is a MWE to reproduce the problem with a much simpler version of ComponentArrays. I’m stumped on this one.

https://discourse.julialang.org/t/help-me-understand-constant-propagation/38822/5?u=jonniedie