Add baseline metrics for lines of code

This commit uses a third party library to estimate the lines of code in
a database that is to be analyzed by codeql.

The estimate uses the same includes and excludes globs for determining
which files should be counted.

The lines of code count is returned by language and injected into the
SARIF as `baseline` property in the `${language}/summary/lines-of-code`
metric.

Author: aeisenberg