Dispose PW instance after running the TestEngine

Description

Disposing playwright assets .Additionally check for disposing the browser instance as well if not already done in any case.

[x] The code change is covered by unit tests. I have added tests that prove my fix is effective or that my feature works
[x] I have performed end-to-end test locally.
[x] New and existing unit tests pass locally with my changes
[x] My changes generate no new warnings
[x] I used clear names for everything
[x] I have performed a self-review of my own code

Package	Line Rate	Branch Rate	Complexity	Health
Microsoft.PowerApps.TestEngine	91%	88%	830	✔
Summary	91% (2218 / 2447)	88% (504 / 570)	830	✔