fix(dev): Add placeholder tsconfigs for tests

[lobsterkatie]

Note: This is an exact duplicate of #5169, which accidentally got merged into the 7.x branch rather than master.

It is well-documented (1, 2, 3, 4, 5, 6) that VSCode doesn't support setups like ours, where multiple tsconfig files coexist in a single directory. Strangely, though, it is only recently that this has become a problem, with VSCode at random intervals forgetting that it's ever heard of expect or describe (because it's not seeing tsconfig.test.json, but taking a while to realize it).

There is an open issue tracking the addition of support for this, but it's been open for a long time, with little movement. In the meantime, this solves the problem by adding placeholder test/tsconfig.json files to each package, each pointing to its corresponding tsconfig.test.ts file. I went with this approach over simply moving and renaming the existing test tsconfigs because this allows us to stay consistent in having all flavors of tsconfig for a package live at the package root level, and provides an easy way to reverse this workaround, should VSCode ever fix the underlying problem.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	19.35 KB (-3.94% 🔽)
@sentry/browser - ES5 CDN Bundle (minified)	59.96 KB (-7.2% 🔽)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	18.17 KB (-3.66% 🔽)
@sentry/browser - ES6 CDN Bundle (minified)	53.58 KB (-7.57% 🔽)
@sentry/browser - Webpack (gzipped + minified)	19.95 KB (-14.16% 🔽)
@sentry/browser - Webpack (minified)	64.95 KB (-20.52% 🔽)
@sentry/react - Webpack (gzipped + minified)	19.97 KB (-14.2% 🔽)
@sentry/nextjs Client - Webpack (gzipped + minified)	43.7 KB (-9.06% 🔽)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	25.35 KB (-2.77% 🔽)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	23.88 KB (-2.48% 🔽)