TYPO3.TypoScript

[!!!][FEATURE] Make TypoScript Context multi-valued; make FlowQuery use explicit

Before, the TypoScript context only contained a single value which was
available in the template as "context". Inside TypoScript Eel expressions, we
automatically wrapped the context object with FlowQuery; so "context" inside
eel expressions was a wrapped context.

Now, we're untangling this:

• The TypoScript context can contain multiple named values, which are all
  directly available inside Eel expressions. So, if your context contains a
  variable "node", this is directly accessible inside Eel.

• FlowQuery must be explicitly used, by calling the "q" function (short for
  "Query").

• The hardcoded "context" variable inside Fluid templates has been removed; so
  all variables which should be available inside Fluid must be explicitly
  passed into the template.

In the context of Phoenix, before this change, one used f.e.
"context.property('title')". Now, he has to use "q(node).property('title')".

Backwards Compatibility =======================

Together with If043a53cb0556ca1d8e72ae05e269dcb8ee056f5, we are inserting a
backwards compatibility layer:

• "context" inside Eel expression is the same as "q(node)", so this is the same
  behavior as before
• "context" inside Fluid Templates is a reference to "node", as it was before.

Still, you should rewrite your templates as we will remove this compatibility
layer later on.

Note: We're merging two features as one change, as it is required in order to
provide backwards compatible behavior.

Resolves: #38631
Resolves: #38633
Change-Id: I5b1863510d372d953c7a076c03214295d4f1131b