Fix/ADF-1166/ESlint errors in core source code

[jsconan]

Related to: https://oat-sa.atlassian.net/browse/ADF-1166

Summary

Fix the ESLint error in the source code for tao-core.

Note: as the changes are pretty heavy, I split them all into several pull requests.

Details

This pull request only targets the core/* part of the library.
The full picture can be seen from the main branch which contains all the fixes: https://github.com/oat-sa/tao-core-sdk-fe.git#fix/ADF-1166/eslint-errors

What has been made:

• fix errors that can be automated using eslint --fix, then adjust the changes in case by case (mostly string literals)
• fix the wrong annotations (missing/wrong return or param definition)
• fix the more complex cases with some refactoring (rest operator instead of .apply())
• replace var by const or let (but not in all places, only in the touched files when it was not adding too much noise)
• apply object shorthand instead of duplicated function names
• apply arrow functions here and there when it helped, but not systematically to reduce the noise

How to test

• checkout and install the source code npm i
• run the linter: npm run lint:src, errors and warnings coming from the core folder should have gone.
• run the unit tests: npm run test core
• install with other repositories, using the following scheme: "@oat-sa/tao-core-sdk": "https://github.com/oat-sa/tao-core-sdk-fe.git#fix/ADF-1166/eslint-errors",, then checking the unit tests and playing with TAO

[github-actions]

Version

Target Version	1.20.2
Last version	1.20.1

There are 0 BREAKING CHANGE, 0 feature, 0 fix

[github-actions]

Coverage Report

Totals
Statements:	90.37% ( 2637 / 2918 )
Methods:	93.62% ( 646 / 690 )

[shaveko]

Looks good, there is eslint report in moduleLoader, but I've found it is addressed in other PR