dependency() does not accept the `main` argument to `dependency('gtest')`

[dcbaker]

Upstream Meson allows the following: dependency('gtest', main : true), which is the same as dependency('gtest_main'), but without having a magical name that might not be expected.

I understand this is probably a very low priority issue, but it's an actual issue I've run into

[annacrombie]

I see that gtest is a dependency with custom lookup functionality. So I could add support for main: true, but I think this issue is really about supporting the custom functionality of gtest which is probably more compilicated than just adding _main to the dep name if main is true?