ESLint Improvements

[lishaduck]

Our ESLint configuration is loosely based on XO.

We should first review what configurations are unnecessary and remove them.

Then, there are a bunch of disabled lint rules.

• [ ] @typescript-eslint/no-unsafe-* (mostly blocked on typescript-eslint/typescript-eslint#1682) (#302)
• [ ] Rules about abusing promises
• [ ] Potential security issues
• [x] unicorn/no-null
• [x] unicorn/prevent-abbreviations (needs a lot of configuration to prevent changing src, etc in variable names)

Next, some tseslint tweaks might be helpful

• [ ] We should enable the recommended-strict tseslint rules
• [ ] Also, strict-boolean-expressions is nice
• [ ] We may wish to consider prefer-readonly
• [x] ban-ts-comment could use some configuring from the default (#217)

Finally, we should consider if these other plugins would be useful:

• [ ] Add eslint-plugin-perfectionist? (~helps object monomorphization, which should help perf very slightly)
• [ ] Add eslint-plugin-no-use-extend-native to prevent messing with messed up prototypes (from XO)
• [ ] Add eslint-plugin-import-x a faster eslint-plugin-import with fewer dependencies (the original is in XO)