Update PHPMailer library to 6.2.0

[jrf]

PHPMailer 6.2.0 has just been released and includes a small fix for PHP 8 compatibility.

The version included with WP should be updated.

Full details:

• ​https://github.com/PHPMailer/PHPMailer/releases/tag/v6.2.0
• ​https://github.com/PHPMailer/PHPMailer/compare/v6.1.8...master

Previously: #51502 (6.1.8), #51311 (6.1.7)

[ayeshrajans]

Tests: ​https://travis-ci.com/github/Ayesh/wordpress-develop/builds/204326555. Similar to the previous updates, we keep three hunks where we force-ignore phpcs checks. This patch updates to the the otherwise identical copy from upstream 6.2.0 tag.

[jrf]

I just reviewed @ayesh's patch and looking at the diff, there is basically no risk, only benefit, so I propose we include this in the WP 5.6 release.

Effectively, there are only four functional changes, three which relate to PHP 8 fixes and one other which doesn't carry any risk either.
Everything else are CS changes.

• ​https://github.com/Ayesh/wordpress-develop/commit/2d5f609d0733785604d4447576edc11f3b39d08a#diff-13bdcb601c2993d3cbeabd8bae18ed1a56390bbfd7dfe0d32bec702cc843a441R1467
• ​https://github.com/Ayesh/wordpress-develop/commit/2d5f609d0733785604d4447576edc11f3b39d08a#diff-13bdcb601c2993d3cbeabd8bae18ed1a56390bbfd7dfe0d32bec702cc843a441R2135
• ​https://github.com/Ayesh/wordpress-develop/commit/2d5f609d0733785604d4447576edc11f3b39d08a#diff-13bdcb601c2993d3cbeabd8bae18ed1a56390bbfd7dfe0d32bec702cc843a441R4531
• ​https://github.com/Ayesh/wordpress-develop/commit/2d5f609d0733785604d4447576edc11f3b39d08a#diff-13bdcb601c2993d3cbeabd8bae18ed1a56390bbfd7dfe0d32bec702cc843a441R4537

[jrf]

Oh and what I nearly forgot to say: thanks @ayeshrajans for the quick turn around on getting a patch ready for this!

[hellofromTonya]

Adding the dev-feedback keyword so this ticket shows up in the "Commit Candidates which need Dev Review" section on Next Major Release, Workflow Oriented report.

[SergeyBiryukov]

In 49713:

External Libraries: Upgrade PHPMailer to version 6.2.0.

For a full list of changes in this update, see the PHPMailer GitHub:
​https://github.com/PHPMailer/PHPMailer/compare/v6.1.8...v6.2.0

Props ayeshrajans, jrf.
Fixes #51874.

[SergeyBiryukov]

Reopening for backporting to the 5.6 branch.

Marking as dev-reviewed, as there is already another committer's review in comment:2.

[SergeyBiryukov]

In 49714:

External Libraries: Upgrade PHPMailer to version 6.2.0.

For a full list of changes in this update, see the PHPMailer GitHub:
​https://github.com/PHPMailer/PHPMailer/compare/v6.1.8...v6.2.0

Props ayeshrajans, jrf.
Reviewed by jrf, SergeyBiryukov.
Merges [49713] to the 5.6 branch.
Fixes #51874.