gl_resource_manager: Add missing noexcept specifiers to move constructors and assignment operators

Standard library containers may use std::move_if_noexcept to perform
move operations. If a move cannot be performed under these
circumstances, then a copy is attempted. Given we only intend for these
types to be move-only this can be somewhat problematic. By defining
these to be noexcept we prevent cases where copies may be attempted.