[llvm] [IR2Vec] Adding tests to check multiple invocations of `getFunctionVector()` and `getInstVecMap()` return same results (PR #162365)

[S. VenkataKeerthy via llvm-commits]

svkeerthy wrote:

> Given the tests only differ by a single enum value, this seems like a good case for use of a value-parameterized test. https://google.github.io/googletest/advanced.html#value-parameterized-tests

Thanks. Will do it for all the applicable tests together in a separate patch. There are many such instances in IR2VecTest.

https://github.com/llvm/llvm-project/pull/162365