Co-authored-by: NPolina Sokolova <polinasok@users.noreply.github.com>

Pulls in v0.3.0 of google/go-dap; this version has some fixes and API
improvements which service/dap will be able to leverage to clean up some
code.

* vendor: update starlark

* terminal: use new mechanism to cancel starlark threads

See: https://github.com/google/starlark-go/pull/298

It is only used in benchmarks and 'go test' now has command line
options to enable profiling as appropriate (but maybe it didn't in
2014).

Fixes #2037

Fixes #2026

Remove gitignore rule preventing vendor/modules.txt file from being
commited, add check that the vendor directory is synchronized.