librenderengine: avoid vector<const T>

A container of const T uses std::allocator<const T>, which was an
undocumented libc++ extension that has been removed.

See https://github.com/llvm/llvm-project/pull/96319.

Bug: 349681543
Test: m librenderengine
Change-Id: I4c0f5adb94415777f832217bc8115e04de6186c5