Move v2/testsuite to v2/internal/testsuite

[pelletier]

@moorereason I'm looking at the exposed API of v2 in preparation for the stable release (finally!). I saw the package v2/testsuite is public. I only see two uses of it:

In gotoml-test-decoder:

go-toml/cmd/gotoml-test-decoder/main.go

Line 9 in 4807229

"github.com/pelletier/go-toml/v2/testsuite"

And toml_testgen_support_test.go:

go-toml/toml_testgen_support_test.go

Line 11 in 4807229

"github.com/pelletier/go-toml/v2/testsuite"

Do you foresee using those functions outside of go-toml or do you mind if I move them to v2/internal/testsuite to avoid making them part of the public API?

[moorereason]

I agree. Let's move it to internal.

If my memory serves me, I was using the API initially to do direct Go differential fuzzing against BurntSushi. I'm now fuzzing the CLI decoders so that I can fuzz against non-Go implementations.

[moorereason]

BTW, we also need to run go generate to regen the tests from the toml-test suite.