Backport Scaladoc jQuery update to 2.12.9?

[lrytz]

Should we backport scala/scala#8179 for 2.12.9?

[lrytz]

Other candidates for backporting:

• Properly escape any HTML in string literals in Scaladoc examples scala#7871
• escape special characters in SyntaxHigh.scala scala#7183
• Java fields don't override each other scala#8158

[eed3si9n]

I have the Scaladoc fixes here - scala/scala#8271

I also looked at scala/scala#8158, but the initial conflict looked like the change might require other prior changes (scala/scala#7941, scala/scala#7929), so I didn't go too deep.

[lrytz]

looked at scala/scala#8158

Oh, I only see now that this issue is a regression in 2.13. Really sorry about that...