Vendor apexes can be "updatable: true"

Vendor APEXes can be updatable unless it sets "use_vndk_as_stable:true".
When "updatable:true", it should meet the "updatable" requirements like
"should set min_sdk_version".

Bug: 274396342
Bug: 274041915
Test: m nothing (soong tests)
Change-Id: I746d8941c21e883c1eba3e1f1e5a414a67db071a

cc/cc.go

@@ -3861,6 +3861,7 @@ func (c *Module) UniqueApexVariations() bool {
 	// When a vendor APEX needs a VNDK lib in it (use_vndk_as_stable: false), it should be a unique
 	// APEX variation. Otherwise, another vendor APEX with use_vndk_as_stable:true may use a wrong
 	// variation of the VNDK lib because APEX variations are merged/grouped.
+	// TODO(b/274401041) Find a way to merge APEX variations for vendor apexes.
 	return c.UseVndk() && c.IsVndk()
 }