[XLA] Allow the tuple simplifier to operate on only subcomputations (#19769)

* Allow the tuple simplifier to operate on only subcomputations

* Remove unnecessary trace

* Add a test for the tuple simplifier

Summary: Adding a test for the tuple simplifier following review of public Pull Request

Test Plan: ran this specific test, and all existing poplar tests

Reviewers: jamesn

Reviewed By: jamesn

Differential Revision: https://phabricator.sourcevertex.net/D4548

* Add comment to the parameter in the default constructor

* Correct clang-tidy linting issue