docs(language-service): update integration test information (#32269)

The documentation for the langauge service plugin integration test
appears to be stale. Remove section about new versions of TypeScript,
which appear not to be tested, and update the information about
generating and updating goldens to reflect the new way of doing so.
Add information about install deps in the repo root, this directory, and
building Angular before testing.

Also remove trailing whitespace on one line.

PR Close #32269

integration/language_service_plugin/README.md

@@ -1,25 +1,21 @@
 # Angular Language Service Test
 
 This directory is an integration test for `@angular/language-service` to ensure
-that various versions of the server can be loaded in the supported versions of 
-TypeScript's language service.
+that the language service works correctly as a `tsserver` plugin.
 
-## New supported version of TypeScript
+To use the tests:
 
-To add a new supported version of TypeScript:
-
-1) Create directory in `typescripts` to hold the new version following the pattern
-   of the other versions.
-2) Add the directory name to the end of the `TYPESCRIPTS` variable in the 
-   `scripts/env.sh` file.
-3) Run `scripts/update_golden.sh` to generate the expected files.
-4) Verify the expected output is reasonable by comparing to a known good output
-   from a previous version.
+- Use `yarn install` to install all dependencies in this directory and in the Angular repo root
+    directory.
+- From the Angular repo root directory, build Angular in the `dist/packages-dist` folder with
+    `./scripts/build-packages-dist.sh`.
+- In this directory, run the tests with `yarn test`.
 
 ## Update golden files
 
-If the expected output needs to be updated run `scripts/update_golden.sh` to
-update the expected output of the server.
+If the expected output needs to be updated, run `yarn golden my-golden.json`, replacing
+`my-golden.json` with the golden file to be updated. Do not qualify the file with a directory path.
+See [generate.ts](./generate.ts) for more information.
 
 ## Adding a new fixture
 
@@ -30,7 +26,7 @@ I also hand modified the input to remove superfluous request.
 
 Once a new fixture is created:
 
-1) Add the fixture base name (without the .json) to `FIXTURES` in 
-   `scripts/env.sh`.
-2) Run `scripts/udpate_golden.sh` to produce the expected output files.
-3) Hand validate the expected output is reasonable.
+1) Add the fixture name to `goldens/`
+2) Run `yarn golden my-golden.json`, replacing `my-golden.json` with the new fixture name, to
+   produce the expected output files.
+3) Hand validate that the expected output is reasonable.