Use dot to separate purpose from validator name in blueprint

The rationale is two folds:

  1. It's more consistent with how we already separate the validator
  name from its module.

  2. Because `_` may be present in Aiken's validator's name, it is hard
     to read and I am afraid it could potentially conflict later on. So
     it's better to use a separator that cannot appear in validator
     names.

examples/acceptance_tests/script_context/v3/ctx/simple_spend/resolved_inputs.template

@@ -1,5 +1,5 @@
 [
-  { 0: h'70{{ simple_spend.simple_spend_spend.hash }}'
+  { 0: h'70{{ simple_spend.simple_spend.spend.hash }}'
   , 1: 1000000000
   , 2: [1, 24(h'd87980')]
   }

examples/acceptance_tests/script_context/v3/ctx/simple_spend/tx.template

@@ -23,7 +23,7 @@
 
     { 5: [[0, 0, 121([]), [1000000, 100000000]]]
 
-    , 7: [h'{{ simple_spend.simple_spend_spend.cbor }}']
+    , 7: [h'{{ simple_spend.simple_spend.spend.cbor }}']
 
     },