Full support for CommonJS auto-imports in JS

[andrewbranch]

In #32684, I added the ability for auto-imports to write a require variable declaration in JS files. However, it didn’t work for named or default exports, and under default project settings, would never be triggered from completions; it was only reachable by code fix. This is particularly problematic for JS, because unless the user has explicitly enabled type checking JS through VS Code settings, a tsconfig or jsconfig file, or // @ts-check, you can’t get code fixes because you don’t get errors.

This PR removes those limitations, and also recognizes members of object literals assigned to module.exports as importable symbols.

How do we choose between import and require for a JS file?

Rules are evaluated in order (highest priority first).

1. If the imported identifier could be added to an existing import, add it there.
2. If the imported identifier could be added to an existing require, add it there.
3. If the importing file contains any ES2015+ import/export syntax, use import.
4. If the importing file contains any CommonJS syntax, use require.
5. If the compiler options indicate a module target of ES2015+, use import.
6. Use require.

How are require variable declarations written for different kinds of exports?

• const { foo } = require('./foo') maps to named ES exports and CommonJS exported object literal members (module.exports = { foo }).
• const { default: foo } = require('./foo') maps to default ES exports (hopefully people aren’t actually doing this).
• const foo = require('./foo') maps to everything else.

Fixes#20292
Fixes#30549

Related:

• No auto imports in new JavaScript file #36611
• import fix / autocomplete requires type checking JS/JSX #36134

[andrewbranch]

This is the fundamental conceptual change in this file, and everything else is basically just implementation details. This enum used to represent final syntax; now it’s more a representation of where the symbol can be found in the module. Whether or not to use JS is then calculated and stored elsewhere, so that

• CommonJS can mean import foo = require('mod') or const foo = require('mod')
• Namespace can mean import * as foo from 'mod' or const foo = require('mod')
• Default can mean import foo from 'mod' or const { default: foo } = require('mod')
• Named can mean import { foo } from 'mod' or const { foo } = require('mod')

[sandersn]

Looks pretty good to me, although I wasn't previously familiar with the importFixes code.