evas textblock: update format nodes when a Evas Textblock Style is updated

evas textblock: update format nodes when a Evas Textblock Style is updated

Summary:
A style tag among a text has to be replcaed by its matched tag when
a format node is created. If the matched tag is changed, format nodes
should be updated.
But, if a style text for Evas Textblock Style is changed,
related format nodes are not updated without setting new text.
The patch changes to update format nodes when new style text is set.
@fix

Test Plan: Included in Evas Test Suite.

Reviewers: raster, tasn, herdsman, subodh6129, zmike

Subscribers: zmike, cedric, z-wony, Blackmole

Tags: #efl

Differential Revision: https://phab.enlightenment.org/D4697

Committer's note: rebased.