[SPIR-V] Integer bitfield is emitted into seperate storage slot, breaking array stride

**Description**
Similar to issue #8470, adding an int type bitfield mixed in with uint bitfields causes separate member slots to be emitted, changing the ArrayStride.

**Steps to Reproduce**
Repro with int bitfield member, ArrayStride is incorrectly 24: https://godbolt.org/z/da48esceE
With uint member instead, ArrayStride is 20 as intended: https://godbolt.org/z/MTq8xanx3
