Dist kernel_version.txt in soong-only builds

This ports some of the kernel version/config extraction code from
make, and updates our handling of kernel_version_for_uffd_gc.txt as
well.

There are a number of differences in the implementation vs how make
implements it. See comments in the source code for more information.

Bug: 398023642
Test: m dist, see kernel_version.txt
Change-Id: I53c9ef12912683585e45da04a44890fff1381398