Add vintf info and userdata size to Soong's misc_info.txt

- vintf info will be read from the global productVariables struct. This
  will likely need to be revisited when we have multiple
android_device's in the tree
- userdata has been special-cased to create a `userdata_size` entry in
  addition to $(filesystem)_partition_size entry. This special case
matches the make misc_info.txt implementation.

Bug: 398036609
Test: Built Soong's misc_info.txt locally
Change-Id: I9f312c8022c5faf84442cb51f1e13043768aed53