rust: Add vendor and recovery dylib support.

Adds dylib support for vendor and recovery images.

This changes the default linkage for vendor and recovery images to
dylib, which matches the platform default linkage. This also means that
by default, dylib-std variants are used for rlib dependencies.

Bug: 204303985
Test: Soong tests.
Test: m dist vendor-snapshot
Test: RECOVERY_SNAPSHOT_VERSION=current m dist recovery-snapshot
Change-Id: If84074b8615a70c45e7e162abeb853dc8c34d49a