Fix name resolution in typealias with constraint (#144)

The body of a typealias gets inlined into wherever the typealias
is used. This fixes a bug where the references in the typealias body can
resolve to the wrong value.

pkl-core/src/test/files/LanguageSnippetTests/output/api/string.pcf

@@ -341,8 +341,8 @@ examples {
     "abcdefg"
     "abcdefg"
     "   abcdefg"
-    "Type constraint `this.length == 1` violated. Value: \"\""
-    "Type constraint `this.length == 1` violated. Value: \"aa\""
+    "Type constraint `length == 1` violated. Value: \"\""
+    "Type constraint `length == 1` violated. Value: \"aa\""
   }
   ["padEnd()"] {
     ""
@@ -351,8 +351,8 @@ examples {
     "abcdefg"
     "abcdefg"
     "abcdefg   "
-    "Type constraint `this.length == 1` violated. Value: \"\""
-    "Type constraint `this.length == 1` violated. Value: \"aa\""
+    "Type constraint `length == 1` violated. Value: \"\""
+    "Type constraint `length == 1` violated. Value: \"aa\""
   }
   ["toBooleanOrNull()"] {
     true

pkl-core/src/test/files/LanguageSnippetTests/output/types/typeAliasConstraint1.pcf

@@ -0,0 +1,2 @@
+res1 = "a"
+res2 = List("a", "b")

pkl-core/src/test/files/LanguageSnippetTests/output/types/typeAliasConstraint2.pcf

@@ -0,0 +1,3 @@
+foo = 1
+bar {}
+qux {}