html: add PrependChild and InsertAfter

[olavfosse]

These methods complement the already existing AppendChild and InsertBefore methods in allowing for easy and safe manipulation of Node trees.

For example code like

oldChild.Parent.InsertBefore(newChild, oldChild.NextSibling)

can now be written like

oldChild.Parent.InsertAfter(newChild, oldChild)

and code like

node.InsertBefore(newNode, node.FirstChild)

can now be written like

node.PrependChild(newNode)

[gopherbot]

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[gopherbot]

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[gopherbot]

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[gopherbot]

Message from Olav Fosse:

Patch Set 1:

(1 comment)

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Message from Olav Fosse:

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(1 comment)

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[olavfosse]

@googlebot I signed it!

[gopherbot]

This PR (HEAD: f7e0d51d255c7971acb9ef9f7ebb4c8476ebecee) has been imported to Gerrit for code review.

Please visit https://go-review.googlesource.com/c/net/+/329734 to see it.

Tip: You can toggle comments from me using the comments slash command (e.g. /comments off) See the Wiki page for more info

[gopherbot]

Message from Olav Fosse:

Patch Set 2:

(1 comment)

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