Add "apex_vndk" module type

"apex_vndk" is a variant of "apex" module.

apex_vndk {
  name: "com.android.vndk",
  ..
}

This rule is used to produce a VNDK APEX per vndk version.
It supports automatic inclusion of vndk libs.

If "vndk_version" property is set, the prebuilt vndk libs of
the version will be included in the apex bundle.

apex_vndk {
  name: "com.android.vndk.v29"
  vndk_version: "29",
  ...
}

Otherwise, platform's vndk version is used.

This will replace /system/{lib}/vndk-{ver} and vndk-sp-{ver}.

Bug: 134357236
Bug: 139772411
Test: m com.android.vndk
Change-Id: Ib5c86e625839389670d13c683a7427198ef6852f