Implement formatting of assert statements

tests/__snapshots__/test_samples/test_samples[sample0][testssamplestest1.zeek].raw

@@ -206,3 +206,10 @@ function comments()
 
 function no_comments()
 	{ }
+
+# Assert.
+function foo()
+	{
+	assert 1 == 2, "One is not two";
+	assert 1 == 1;
+	}

tests/samples/test1.zeek

@@ -173,4 +173,9 @@ function no_comments()
        {
        }
 
+# Assert.
+function foo() {
+assert 1 == 2, "One is not two";
+assert 1 == 1;
+}
 

zeekscript/formatter.py

@@ -1027,6 +1027,12 @@ def format(self):
             self._format_child()  # <preproc_directive>
             self._write_nl()
 
+        elif start_token == "assert":
+            self._format_child()  # 'assert'
+            self._write_sp()
+            self._format_children()
+            self._write_nl()
+
         elif start_token == ";":
             self._format_child(hints=Hint.NO_LB_BEFORE)  # ';'
             self._write_nl()
@@ -1087,6 +1093,10 @@ def format(self):
         self._format_child(hints=Hint.NO_LB_BEFORE)  # ')'
 
 
+class AssertMsgFormatter(SpaceSeparatedFormatter):
+    pass
+
+
 class ExprFormatter(SpaceSeparatedFormatter, ComplexSequenceFormatterMixin):
     # Like statments, expressions aren't currently broken into specific symbol
     # types, so we use helpers or parse into them to identify what particular