LineDecorationAttachment: revert to using unsafe react methods
Created by: lguychard
Fixes #5236
The changes introduced to comply with react/no-unsafe
in https://github.com/sourcegraph/sourcegraph/pull/5072 broke the initial display of after-line decorations. This reverts to using UNSAFE_componentWillMount()
and UNSAFE_componentWillReceiveProps()
, with an explanatory comment.