Fix specialization constant patching on D3D12.

[blueskythlikesclouds]

Fixes #100138.

The specialization constant patching code was rejecting signed values, assuming it needed to set the MSB to respect LLVM IR's VBR encoding. However, as explained here, the contents of the integer actually do not matter at all, because we can just keep emitting continue bits even if the bits are all zero.

Godot already uses an appropriate sentinel value to enforce 32 bits in the output bytecode, so this approach works fine.

[clayjohn]

seems fine to me

[Repiteo]

Local dev builds fail from the sign change. Given the lambda already expects a uint64_t, we should be doing the same with the base variable

[Repiteo]

Thanks!