target/i386/mshv: Implement mshv_get_standard_regs()

target/i386/mshv: Implement mshv_get_standard_regs()

Fetch standard register state from MSHV vCPUs to support debugging,
migration, and other introspection features in QEMU.

Fetch standard register state from a MHSV vCPU's. A generic get_regs()
function and a mapper to map the different register representations are
introduced.

Signed-off-by: Magnus Kulke <magnuskulke@linux.microsoft.com>
Link: https://lore.kernel.org/r/20250916164847.77883-15-magnuskulke@linux.microsoft.com
[mshv.h/mshv_int.h split. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>