This commit speeds up the tests by calling `MockHost.reset()` in
`beforeEach()` instead of destroying the entire language service and
creating a new one. The creation of a new language service instance is
expensive due to the need to initialize many core Symbols when creating
a new program.
This speeds ups the test (on my local machine) from 35 secs to 15 secs.
PR Close#33200
11bf7679a1