feat(driver): Replace value.Value with Value() return

[simamumu]

resolve: #138

If you are ok with the content of #138, please use this PR.

[rahul2393]

@simamumu Can you please fix the failing integration tests?

[simamumu]

Sorry, I missed the failing test...
I will fix the tests (but not until after 2/18 as I can't write the code now)

[simamumu]

@rahul2393
The test was failing because typed nil params such as spanner.NullInt64 were converted to nil by the Value method, so the paramTypes in ExecuteSqlRequest did not match.

The following modifications were made to the code as intended by the test

1. Do early returns for defined types such as spanner.NullInt64 and do not check/execute Value().
2. Types that implement the Valuer interface execute Value() and replace it.
3. If the Valuer interface is not implemented, or the return value of Value() is not the expected type, return an unsupported value error.

I have confirmed that the test passes locally.

please re-review code 🙏

[kdvy]

@simamumu - We would find this support useful as well. Would you be able to merge ?