_test module types shouldn't override user-set test property

Android lint considers code "test" code depending on if the --test flag
is passed. We pass it by default for *_test module types, but also allow
the user to control it via the "lint: { test: true }" property. However,
the module types were overriding the user-defined test property if
the user-defined one was supplied via a defaults module. Split the
test property into two so that modules can use a separate lower priority
one from the user-controlled one.

Fixes: 358643466
Test: m nothing --no-skip-soong-tests
Change-Id: I1b1ef7a73ca9f413aa29e0c6025134fc52dc7caf