fix: support require to internal files without explicitly writing .js in the path

[giladgd]

Description of change

Support using require on internal module files without explicitly writing .js at the end of the path.

For example, this code would work now:

// in ESM projects
import {snakeCase} from "typeorm/util/StringUtils.js";

// in CommonJS projects
const {snakeCase: snakeCase1} = require("typeorm/util/StringUtils"); // this line previously thrown an error, this PR fixes that
const {snakeCase: snakeCase2} = require("typeorm/util/StringUtils.js");

console.log(snakeCase === snakeCase1); // true
console.log(snakeCase === snakeCase2); // true

Closes #8656
Closes tonivj5/typeorm-naming-strategies#16

Pull-Request Checklist

• Code is up-to-date with the master branch
• npm run lint passes with this change
• npm run test passes with this change
• This pull request links relevant issues as Fixes #0000
• There are new or updated unit tests validating the change - The change in this PR is hard to create a test for from within the module itself, since the exports property in package.json only reflects imports of the module from the outside, and does not affect internal file imports
• Documentation has been updated to reflect this change - N/A
• The new commits follow conventions explained in CONTRIBUTING.md

[giladgd]

This is needed since the new "./*" definition would make importing of "typeorm/browser" look for node_modules/typeorm/browser.js instead of node_modules/typeorm/browser/index.js, so this property makes sure importing "typeorm/browser" continues to work properly