fix(coverage): merge coverage ranges (#13334)

Covered ranges were not merged and thus it appeared that some lines
might be uncovered. To fix this I used "v8-coverage" that takes care
of merging the ranges properly. With this change, coverage collected
from a file by multiple entrypoints is now correctly calculated.

I ended up forking https://github.com/demurgos/v8-coverage and adding
"cli/tools/coverage/merge.rs" and "cli/tools/coverage/range_tree.rs".

1 files changed, 6 insertions, 0 deletions

diff --git a/cli/tests/testdata/coverage/multifile/mod.js b/cli/tests/testdata/coverage/multifile/mod.js
new file mode 100644
index 000000000..b9f8d627a
--- /dev/null
+++ b/cli/tests/testdata/coverage/multifile/mod.js
@@ -0,0 +1,6 @@
+export function test(a) {
+  if (a) {
+    return 0;
+  }
+  return 1;
+}