Add struct instantiation support to wgsl-in (#507)

* Add struct instantiation support to wgsl-in

* Readd type matching and move struct test

* rebase onto master and update tests

* Update tests to upstream

* Fix merge errors

* Rebase onto master

* [wgsl-in] delay composite type creation

* Use the new WGSL construction syntax in the tests

Co-authored-by: Dzmitry Malyshau <kvarkus@gmail.com>