target/i386/mshv: Implement mshv_vcpu_run()

target/i386/mshv: Implement mshv_vcpu_run()

Add the main vCPU execution loop for MSHV using the MSHV_RUN_VP ioctl.

The execution loop handles guest entry and VM exits. There are handlers for
memory r/w, PIO and MMIO to which the exit events are dispatched.

In case of MMIO the i386 instruction decoder/emulator is invoked to
perform the operation in user space.

Signed-off-by: Magnus Kulke <magnuskulke@linux.microsoft.com>
Link: https://lore.kernel.org/r/20250916164847.77883-23-magnuskulke@linux.microsoft.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>