support TypeScript

[unional]

In TypeScript, one of the questions I always have is whether to use the importHelpers flag.

Should I use it depends on the project. If the project is big, then using importHelpers will reduce the size of the package.

However the threshold is unknown and it is difficult to test.

If size-limit can support TypeScript directly, when we can easily test it:

{
  "size-limit": [
    { "type": "typescript", "path": "./src/index.ts", "tsconfigPath": "tsconfig.withoutHelper.json", "limit": "10kB" },
    { "type": "typescript", "path": "./src/index.ts", "tsconfigPath": "tsconfig.withHelper.json", "limit": "10kB" }
  ]
}