feat(duckdb): Add transpilation support for COLLATION function

Author: fivetran-amrutabhimsenayachit

sqlglot-integration-tests

@@ -2962,6 +2962,13 @@ def chr_sql(self, expression: exp.Chr, name: str = "CHR") -> str:
             arg = exp.cast(arg, exp.DType.INT)
         return self.func("CHR", arg)
 
+    def collation_sql(self, expression: exp.Collation) -> str:
+        this = expression.this
+        if isinstance(this, exp.Collate) and this.expression.name:
+            return self.sql(this.expression)
+        self.unsupported("COLLATION function is not supported by DuckDB")
+        return self.sql(exp.null())
+
     def _validate_regexp_flags(
         self, flags: t.Optional[exp.Expr], supported_flags: str
     ) -> t.Optional[str]: