insertAdjacent* methods should be part of the Element interface

[mhegazy]

From @davidkmenta on June 30, 2016 14:16

TypeScript Version: 1.8.10

Expected behavior: According to the MDN (https://developer.mozilla.org/en-US/docs/Web/API/Element), insertAdjacent* methods should be part of the Element interface.

Actual behavior: insertAdjacent* methods are part of the HTMLElement interface.

Copied from original issue: microsoft/TypeScript-DOM-lib-generator#130