Stop using pg_attrdef.adsrc, obsoleted in PG12

Use pg_get_expr() on adbin instead

Fixes #138

Author: roji

EF6.PG/Resources/NpgsqlSchema.ssdl

@@ -57,7 +57,7 @@
         end as is_identity,
         false as is_generated,
 -- default value column
-        ad.adsrc as default_value
+        pg_get_expr(ad.adbin, ad.adrelid) as default_value
         from pg_attribute a
           join pg_class c
           on a.attrelid = c.oid
@@ -178,7 +178,7 @@
         end as is_identity,
         false as is_generated,
 -- default value column
-        ad.adsrc as default_value
+        pg_get_expr(ad.adbin, ad.adrelid) as default_value
         from pg_attribute a
           join pg_class c
           on a.attrelid = c.oid

EF6.PG/Resources/NpgsqlSchemaV3.ssdl

@@ -57,7 +57,7 @@
         end as is_identity,
         false as is_generated,
 -- default value column
-        ad.adsrc as default_value
+        pg_get_expr(ad.adbin, ad.adrelid) as default_value
         from pg_attribute a
           join pg_class c
           on a.attrelid = c.oid
@@ -178,7 +178,7 @@
         end as is_identity,
         false as is_generated,
 -- default value column
-        ad.adsrc as default_value
+        pg_get_expr(ad.adbin, ad.adrelid) as default_value
         from pg_attribute a
           join pg_class c
           on a.attrelid = c.oid