Moving to gtest allows negative test cases as the current parser
implementation exits the process on a parser error. The CL adds two
small negative tests. The idea is less to get full coverage, but to
have a place for regression tests.

Drive-by-change: Lexer errors need a valid source position scope and
Json parser needs a valid SourceId, otherwise we read OOB when the
error message is generated.

R=petermarshall@chromium.org

Bug: v8:8880
Change-Id: I56c4b9e0a29c8333b2e5e44f8116e5178552d2f0
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1498472Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Commit-Queue: Simon Zünd <szuend@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60014}