Support statement coverage

I think the Node.js coverage reporter should include support for reporting statement coverage.

My idea is to parse the source code into an Abstract Syntax Tree (AST) using acorn-walk, and then use the Statement callback to extract statements. They could then be converted to CoverageStatements, (similarly to how the getLines function works with lines to CoverageLines).

These statements could then be mapped to ranges in the same way that lines are handled in mapRangeToLines.

I saw a (extremely complicated) way of doing this in https://github.com/cenfun/monocart-coverage-reports/, so it appears to be possible.

从 Node.js 覆盖率报告器开始，了解 getLines 如何生成 CoverageLines，以及 mapRangeToLines 如何处理范围。定义语句提取和范围映射要求，然后验证报告器是否在现有行覆盖率之外输出语句覆盖率。