[analysis_server] Make format of LSP completion tests more consistent

No functional changes here, only formatting/code style:

- Remove additional intending from embedded code in some tests (which didn't match others in this file or the style of other tests in the server)
- Change expression-bodied-tests to block bodies where they're not on a single line

Change-Id: I2c15bbcf7b7accff85f34a4e9ad5afa3e0a0a221
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/408820
Reviewed-by: Brian Wilkerson <[email protected]>
Reviewed-by: Phil Quitslund <[email protected]>
Commit-Queue: Phil Quitslund <[email protected]>

Author: DanTup