Fix bug 10298 CTFE wrong code for struct array literal init

The elements in an array literal need to have constness
implicitly cast away when they are being slice assigned.
fix Issue 10354 - DIP37: ICE with using indirectly imported template through package.d
Merge pull request #2177 from 9rnsr/fix10354

Issue 10354 - DIP37: ICE with using indirectly imported template through package.d
Merge pull request #2172 from donc/ctfe10298structarrayinit

10298 CTFE wrong code bug that Walter found