Make libtest_* deps explicit in BUILD files

This is currently implicitly added by the cc_test macro. This can cause
duplicate issues if users write a BUILD file as
```
cc_test (
  name = "mytest",
  deps = ["libgtest"],
)
```
Making this dep explicit in BUILD files prevents this issue.

The property `gtest` will not be removed as part of this CL. cc_test
macro will use this property to add some gtest specific copts

Test: unit tests
Bug: 249374572
Change-Id: Ife931e26367fd4aab302bedc709cf907e2c01245