feat: sql handlers for custom media types

* test text/html and drop HtmlRawOutputSpec.hs
* all tests passing, removed all pendingWith
* make functions compatible with pg <= 12
* move custom media types tests to own spec
* anyelement aggregate
* apply aggregates without a final function
* overriding works
* overriding anyelement with particular agg
* cannot override vendored media types
* plan spec works with custom aggregate
* renamed media types to make clear which ones are overridable
* correct content negotiation with same weight
* text/tab-separated-values media type
* text/csv with BOM plus content-disposition header

src/PostgREST/SchemaCache/Identifiers.hs

@@ -3,6 +3,8 @@
 
 module PostgREST.SchemaCache.Identifiers
   ( QualifiedIdentifier(..)
+  , RelIdentifier(..)
+  , isAnyElement
   , Schema
   , TableName
   , FieldName
@@ -17,6 +19,9 @@ import qualified Data.Text  as T
 
 import Protolude
 
+data RelIdentifier = RelId QualifiedIdentifier | RelAnyElement
+  deriving (Eq, Ord, Generic, JSON.ToJSON, JSON.ToJSONKey)
+instance Hashable RelIdentifier
 
 -- | Represents a pg identifier with a prepended schema name "schema.table".
 -- When qiSchema is "", the schema is defined by the pg search_path.
@@ -28,6 +33,9 @@ data QualifiedIdentifier = QualifiedIdentifier
 
 instance Hashable QualifiedIdentifier
 
+isAnyElement :: QualifiedIdentifier -> Bool
+isAnyElement y = QualifiedIdentifier "pg_catalog" "anyelement" == y
+
 dumpQi :: QualifiedIdentifier -> Text
 dumpQi (QualifiedIdentifier s i) =
   (if T.null s then mempty else s <> ".") <> i