Add event placeholder support to more fields (#6098)

* Add event placeholder support to more fields

I found it useful to be able to use the `{event}` placeholder in
some fields such as the "End of presale text" because I don't need
to fix the texts creating a new event by cloning another event.
I made placeholders available to the other fields as well (where not too
difficult). Specifically `presale_has_ended_text`, `voucher_explanation_text`
`banner_text`, `banner_text_bottom` and `event_info_text`.
In addition, I grouped them under a new `texts` variable in the `context`
(including `frontpage_text` which was part of the root `context` previously).

* change compute location

---------

Co-authored-by: Raphael Michel <michel@rami.io>

src/pretix/base/pdf.py

@@ -77,6 +77,7 @@ from reportlab.platypus import Paragraph
 
 from pretix.base.i18n import language
 from pretix.base.models import Checkin, Event, Order, OrderPosition, Question
+from pretix.base.services.placeholders import PlaceholderContext
 from pretix.base.settings import PERSON_NAME_SCHEMES
 from pretix.base.signals import layout_image_variables, layout_text_variables
 from pretix.base.templatetags.money import money_filter
@@ -401,11 +402,7 @@ DEFAULT_VARIABLES = OrderedDict((
         "editor_sample": _("Event organizer info text"),
         "evaluate": lambda op, order, ev: str(order.event.settings.organizer_info_text)
     }),
-    ("event_info_text", {
-        "label": _("Event info text"),
-        "editor_sample": _("Event info text"),
-        "evaluate": lambda op, order, ev: str(order.event.settings.event_info_text)
-    }),
+    ("event_info_text", {}),  # Placeholder to "reserve" position, defined later in `get_variables`
     ("now_date", {
         "label": _("Printing date"),
         "editor_sample": _("2017-05-31"),
@@ -670,6 +667,14 @@ def get_images(event):
 def get_variables(event):
     v = copy.copy(DEFAULT_VARIABLES)
 
+    templating_context = PlaceholderContext(event=event)
+    v['event_info_text'] = {
+        "label": _("Event info text"),
+        "editor_sample": _("Event info text"),
+        "evaluate": lambda op, order, ev:
+            templating_context.format(str(order.event.settings.event_info_text))
+    }
+
     scheme = PERSON_NAME_SCHEMES[event.settings.name_scheme]
 
     concatenation_for_salutation = scheme.get("concatenation_for_salutation", scheme["concatenation"])