[SE-3745]: Cherry picks 2020-12-03 XSS security fixes from upstream

[eLRuLL]

This cherry-picks security updates and fixes from https://github.com/edx/edx-platform/pull/25786 which are the same shared as patch for the 2020-12-03 XSS security fixes.

Testing Instructions:

• Make sure the changes reflect the patch shared from edx
• Check Instance is working correctly: https://pr297.sandbox.stage.opencraft.hosting/ (follow instance checklist)

Reviewers

• @s0b0lev

[lgp171188]

@eLRuLL, can you cherry-pick the single squashed commit containing the backported changes to the open-release/juniper.master branch with the -x option instead of cherry-picking multiple commits from the master? I will set up a sandbox to test this PR once you do that and then approve it.

[nizarmah]

@eLRuLL here's the commit hash that you'll need to cherry-pick c03857b78d6204ed3b9a3093367348ebfaaf7d04
I would have done it, but I didn't want to rebase your branch without you approving first.

[s0b0lev]

@eLRuLL you mentioned me as a reviewer for this PR. I have followed the testing checklist - instance pr297 works as expected.

It looks like commits were squashed (as Nizar already mentioned).

I will leave this PR review to @lgp171188.

Let me know @lgp171188 if you wont have time to make a review:

I will set up a sandbox to test this PR once you do that and then approve it.

[eLRuLL]

@lgp171188 @nizarmah sorry about that I didn't check the releases, only saw the change on master and started getting the commits.

@lgp171188 this should be ready to test

ty @s0b0lev for the review btw

[lgp171188]

@eLRuLL, can you cherry-pick with the -x flag so that the commit message contains the hash of the source commit?

[eLRuLL]

oops, I forgot about that, @lgp171188 done

[lgp171188]

@eLRuLL, I have created a sandbox for testing this PR. Once it finishes provisioning, I will approve this PR and merge it.

[lgp171188]

👍

• I tested this and verified that this is a clean cherry-pick of the upstream fix and tested the changes on a sandbox and found no issues.
• I read through the code NA
• I checked for accessibility issues NA
• Includes documentation NA