ensure backward compatibility for Web3 constructor

[Muhammad-Altabba]

Description

Fixes #(5196)

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• I have selected the correct base branch.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• Any dependent changes have been merged and published in downstream modules.
• I ran npm run dtslint with success and extended the tests and types if necessary.
• I ran npm run test:cov and my test cases cover all the lines and branches of the added code.
• I ran yarn run build with success.
• I have tested the built dist/web3.min.js in a browser.
• I have tested my code on the live network.
• I have checked the Deploy Preview and it looks correct.
• I have updated the CHANGELOG.md file in the root folder.

[nazarhussain]

Please make this change to every default export in all the packages.

[Muhammad-Altabba]

With the last commit, the export and import behaves exactly as it was in version 1.x (this is as far as I know. And let me know if this is not true) 😄

However, this also means that the types inside web3 package are no longer exported. So, I recommend having a follow-up task to put those types possibly at web3-core. This can be done perhaps in beta or at a later version. And this could be done along with the refactoring proposed at #5223, or separately.

The line, where the comment was on, has been deleted

[nazarhussain]

Apart form the mentioned change, we need to apply same changes to all packages which are using export default.

[jdevcs]

lgtm, plus we should add simplest blackbox tests as well #5261 as part of new PR