Add cfi static libraries to vendor snapshot

CFI modules can't link against non-CFI static libraries, and vice versa.
So without capturing both CFI and non-CFI static libraries, vendor
modules won't be able to use CFI, which will be a critical security
hole.

This captures both CFI and non-CFI variants of all static libraries for
vendor snapshot, except for those whose cfi are explicitly disabled.

For example, suppose that "libfoo" is defined as follows.

cc_library_static {
    name: "libfoo",
    vendor_available: true,
}

As it doesn't have cfi disabled, two libraries "libfoo.a" and
"libfoo.cfi.a" will be captured. When installed, vendor snapshot module
for "libfoo" will look like:

vendor_snapshot_static {
    name: "libfoo",
    src: "libfoo.a",
    cfi: {
        src: "libfoo.cfi.a",
    },
}

The build system will recognize the "cfi" property, and will create both
CFI and non-CFI variant, allowing any modules to link against "libfoo"
safely, no matter whether CFI is enabled or not.

Two clarification:

1) The reason why we don't create separate modules is that DepsMutator
runs before sanitize mutators. CFI and non-CFI variant of a library
should exist in a single module.

2) We can't capture CFI variant if the source module explicitly disables
cfi variant by specifying the following.

sanitize: {
    cfi: false,
}

In this case, only non-CFI variant will be created for the vendor
snapshot module.

Bug: 65377115
Test: m dist vendor-snapshot && install && build against snapshot
Change-Id: Idbf3e3205d581800d6093c8d6cf6152374129ba4