Set stdio ownership based on the container's user to ensure the
user can open/read/write to/from stdios.
1. stdios in the host are changed to have the owner be the same
uid/gid of the process running the sandbox. This ensures that the
sandbox has full control over it.
2. stdios owner owner inside the sandbox is changed to match the
container's user to give access inside the container and make it
behave the same as runc.
Fixes#6180
PiperOrigin-RevId: 384347009
VFS1 and VFS2 host FDs have different dupping behavior,
making error prone to code for both. Change the contract
so that FDs are released as they are used, so the caller
can simple defer a block that closes all remaining files.
This also addresses handling of partial failures.
With this fix, more VFS2 tests can be enabled.
Updates #1487
PiperOrigin-RevId: 330112266
