ssrFixStacktrace generates incorrect stack traces in Node 12

[Rich-Harris]

Describe the bug

Calling ssrFixStacktrace(error) where the original stack trace goes through line 1 or 2 (where the line number is 1-based) will result in this error if you're using Node 12:

TypeError: Line must be greater than or equal to 1, got -1

That's because of this line:

vite/packages/vite/src/node/ssr/ssrStacktrace.ts

Line 27 in b204bcb

line: Number(line) - 2,

In Node 12, stack traces are accurate, as though the anonymous function wrapper didn't exist:

const fn = new Function(`throw new Error('nope');n//# sourceURL=test.js`);
fn();

// in Node 12
// Uncaught Error: nope
//    at eval (test.js:1:7)

// in Node 13 and later
// Uncaught Error: nope
//    at eval (test.js:3:7)

Because of that, subtracting 2 is unnecessary. But it is necessary in 13 and later.

If the original doesn't go through line 1 or 2, no error will be raised, but the sourcemapped stack trace will be incorrect.

Reproduction

https://github.com/Rich-Harris/vite-repro-ssr-fix-stacktrace

System Info

• vite version: 2.0.3
• Operating System: MacOS
• Node version: 12
• Package manager (npm/yarn/pnpm) and version: npm 7.0.3