Allow VNDK-SP extensions to use vendor lib

This commit changes the VNDK-SP dependencies check.  With the commit,
VNDK-SP-Ext can link to non-VNDK vendor shared libs.  This commit also
refines the "cc_test" so that more error handling cases are properly
tested.

Before this commit, VNDK-SP-Ext could not depend on vendor libs.  It
was disallowed because there were no correct way to load vendor libs.
The fallback link had to specify the shared lib names.  On the other
hand, adding "/vendor/${LIB}" to search paths will lead to
double-loading issue.

In aosp/595067, "allow_all_shared_libs" was added to bionic dynamic
linker.  Now, we can link the "vndk" namespace to "sphal" namespace.
Thus, like VNDK-Ext, VNDK-SP-Ext can link to vendor libs now.

Bug: 77249955
Test: lunch aosp_walleye-userdebug && make -j8  # runs unit tests
Test: lunch aosp_sailfish-userdebug && make -j8  # runs unit tests
Test: Create a VNDK-SP-Ext, link to vendor libs, and run it.
Change-Id: I5511204539a22c998528111076f46756807faf29