[llvm] [SandboxIR] Clean up tracking code with the help of tryTrack() (PR #102406)

[via llvm-commits]

vporpo wrote:

> hmm, at a first glance this seems a bit too magical, it's not clear that tryTrack is basically make_unique. it's hard to suggest something that isn't so magical though...

True. We could perhaps rename it to something like `tryAppendNewChange` ?

https://github.com/llvm/llvm-project/pull/102406