build: update to TS v5

[RebeccaStevens]

PR Checklist

• Addresses an existing open issue
• That issue was marked as status: accepting prs
• Steps in CONTRIBUTING.md were taken

Overview

• Set minimum supported version of TS to v5
• Removes things that have become deprecated in v5
• Uses new bundler strategy for moduleResolution
  • Removes use of .js extensions and /index paths as the bundler resolution now handles that (linting rules updated accordingly).

[JoshuaKGoldberg]

In theory, I love this - easier imports, lots of removed functions, nice clean minimum TypeScript version.

In practice, microsoft/TypeScript#51362 notes that TS v5 comes out in a month, on March 14th. So folks will be in a hard position till then: either they stay on tsutils, stay on an older version of ts-api-utils, or use a beta version of TypeScript. What do you think about waiting till then @RebeccaStevens?

cc @bradzacher from typescript-eslint/typescript-eslint#6380 & typescript-eslint/typescript-eslint#6459, would the typescript@5 requirement be inconvenient to you?

[RebeccaStevens]

To me, waiting a month before making a 1.0 release is no big deal - it gives us plenty of time to get this library right. I guess it really just depends on when typescript-eslint want to release v6.

[bradzacher]

Making it the minimum would prevent us from using it really because we support older TS versions.

[RebeccaStevens]

We don't actually rely on any v5 things so I guess we don't need to set the minimum version to v5.
We can just design the utility functions around v5 and then add any v4 one needed by typescript-eslint or other dependents. Or if we re-export/redefine type guards already defined in TypeScript (#51), then we can easily support older version of TypeScript.

[bradzacher]

For context as of our upcoming v6 release (which is when we'll switch to this package) we'll be bumping the minimum TS version to 4.2 - which is the same minimum that DefinitelyTyped supports.

So we could do the same thing here and keep everything perfectly balanced, as all things should be.

[JoshuaKGoldberg]

I like keeping the minimum TS version synced to DefinitelyTyped and typescript-eslint, if these can all be the same.

[bradzacher]

In order to maintain safety in the codebase we use patch-package to edit the TS types to help flag when we use things that aren't in older versions. I think it's a great strategy we could use here if needs be.