Set target to ES2018

[RaananW]

Based on feedback and babylon native needs I am moving the target for our es packages to es2018

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To prevent this PR from going to the changelog marked it with the "skip changelog" label.

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Snapshot stored with reference name:
refs/pull/13086/merge

Test environment:
https://babylonsnapshots.z22.web.core.windows.net/refs/pull/13086/merge/index.html

To test a playground add it to the URL, for example:

https://babylonsnapshots.z22.web.core.windows.net/refs/pull/13086/merge/index.html#WGZLGJ#4600

Links to test babylon tools with this snapshot:

https://playground.babylonjs.com/?snapshot=refs/pull/13086/merge
https://sandbox.babylonjs.com/?snapshot=refs/pull/13086/merge
https://gui.babylonjs.com/?snapshot=refs/pull/13086/merge
https://nme.babylonjs.com/?snapshot=refs/pull/13086/merge

To test the snapshot in the playground with a playground ID add it after the snapshot query string:

https://playground.babylonjs.com/?snapshot=refs/pull/13086/merge#BCU1XR#0

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Visualization tests for webgl2 have failed. If some tests failed because the snapshots do not match, the report can be found at

https://babylonsnapshots.z22.web.core.windows.net/refs/pull/13086/merge/testResults/webgl2/index.html

If tests were successful afterwards, this report might not be available anymore.