Firefox-ios: FXIOS-465 ⁃ FxA web view memory leak

[garvankeeley]

I see this webview being leaked when debugging (attaching to the webview with Safari).

┆Issue is synchronized with this Jira Task

[kaylagalway]

@garvankeeley Just locally checked out the commit on master(hash db723761e7feed981ffdabdbd4e962822e6275bc) from before my QR code work was merged and opened the memory graph debugger, and it seems this view controller was leaking before those changes. I'm still going to try to figure out where it is coming from, but for now it seems to me like this is not a regression.

[tsuiyuenhong]

Hi, @garvankeeley. I found that FxAWebViewController exists a memory leak.

self -> webview -> configuration -> userContentController -> self

[garvankeeley]

Nice find! Do you want me to assign the bug to you?

[tsuiyuenhong]

Nice find! Do you want me to assign the bug to you?

OK, I have created a PR -> https://github.com/mozilla-mobile/firefox-ios/pull/7071