[FIX] web_editor: the dirty flag is set for character escaping

Reproduction:
1. Install Note, create a new note
2. Start the Inspector, edit the placeholder <p> element in the
description
3. Replace the element as `<p style="color: rgb(32, 31, 30); font-family
: &quot;Segoe UI&quot;, &quot;Segoe UI Web (West European)&quot;, &quot;
Segoe UI&quot;, -apple-system, BlinkMacSystemFont, Roboto, &quot;Helveti
ca Neue&quot;, sans-serif; font-size: 15px;">dsfhislahflidsahisa</p>`
4. The saving icon appears, click it but it will always be there, e.g.
always dirty

Fix: instead of comparing the raw value of the prop value and editing
value, we parse them and compare after the parsing

opw-3341605
task-3434080

closes odoo/odoo#129173

Signed-off-by: David Monjoie (dmo) <dmo@odoo.com>