[!!!][FEATURE] Avoid TSFE->config['config']

Frontend TypoScript has two special details, next to
'configuration' ("constants") and 'setup'.

First, there is the determined "PAGE" object that depends
on type / typeNum. It allows to render multiple different
variants of a pages content. Historically, this has often
been a "print" view, nowadays, this is usually a "json"
variant, or some XML for sitemaps.

A frontend is not rendered without a proper PAGE object.
The FE rendering chain determines the given 'type' and maps
it to a configured PAGE with this 'typeNum', defaulting
to zero '0'.
The patch models the determined PAGE object to the Request
attribute 'FrontendTypoScript' now, which is used by FE
RequestHandler to manage rendering of this PAGE type.

Second special thing is 'config' TypoScript as top-level
'config' settings. Those can be overridden by the specific
PAGE object (often 'page.config'). A typical use case is
'json.config.disableAllHeaderCode = 1'.
This "merged" 'config' array has been availa...