ref(node): store split file in cache for contextlines

[JonasBa]

We were storing the file as a raw string in cache and performing the .split(\n) inside our for(frame of frames) loop... This means that for stack traces with functions belonging to the same file, the file was split multiple times - this is inefficient and we can do better by storing the file as it's split version in cache and avoiding the unnecessary duplicate split operations.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	20.15 KB (+0.16% 🔺)
@sentry/browser - ES5 CDN Bundle (minified)	62.63 KB (+0.18% 🔺)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	18.79 KB (+0.16% 🔺)
@sentry/browser - ES6 CDN Bundle (minified)	55.61 KB (+0.21% 🔺)
@sentry/browser - Webpack (gzipped + minified)	20.53 KB (+0.18% 🔺)
@sentry/browser - Webpack (minified)	67.1 KB (+0.17% 🔺)
@sentry/react - Webpack (gzipped + minified)	20.56 KB (+0.17% 🔺)
@sentry/nextjs Client - Webpack (gzipped + minified)	48.3 KB (+0.07% 🔺)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	27.29 KB (+0.11% 🔺)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	25.55 KB (+0.14% 🔺)
@sentry/replay ES6 CDN Bundle (gzipped + minified)	43.15 KB (+0.08% 🔺)
@sentry/replay - Webpack (gzipped + minified)	37.16 KB (0%)
@sentry/browser + @sentry/tracing + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	60.94 KB (+0.06% 🔺)
@sentry/browser + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	54.26 KB (+0.06% 🔺)