6.4.0-alpha.2

fix(chat): Run adoptPageStyles on theme swap (#1950)

This commit addresses several scenarios where
the old implementation would fail:

1. A runtime change of the global theme. Since
the theme controller overwrites the adopted stylesheets
collection this would nuke previous root styles.

2. SPA router navigation where the chat is created
before a certain framework passes down the 'options'
object.