Rule no-unnecessary-type-assertion doesn't work if tsconfig has "strict": true

[guidsdo]

Bug Report

Rule no-unnecessary-type-assertion doesn't work if your tsconfig.json has "strict": true. It was made so that it only works if you have "strictNullChecks": true but should also work for "strict": true since that covers all strict rules.

Bug introduction: b836f28#diff-2237d1e758ab18614b7d976b89e56ea0R53
Strict rule explanation: https://www.typescriptlang.org/docs/handbook/compiler-options.html

Note, will fix this myself so PR incoming.

Reproduction using TSLint Playground

Playground doesn't allow you to change the tsconfig?

TypeScript code being linted

tsconfig.json

{
  "compilerOptions": {
    /* Enable all strict type-checking options. */
    "strict": true,
    /* Enable strict null checks. */
    // "strictNullChecks": true
  }
}

Code

const x = "y";
x!.length;

with tslint.json configuration:

{
  "defaultSeverity": "error",
  "rules": {
    "no-unnecessary-type-assertion": true
  }
}

Actual behavior

No errors.

Expected behavior

An error!

[JoshuaKGoldberg]

🤖 Beep boop! 👉 TSLint is deprecated 👈 and you should switch to typescript-eslint! 🤖

🔒 This issue is being locked to prevent further unnecessary discussions. Thank you! 👋