(un)reachable functions: normalize JSON and XML keys

JSON uses camelCase, XML uses underscores or dashes (we liberally mix
them across the code base).

Author: tautschnig

regression/goto-analyzer/unreachable-functions-basic-json/test.desc

@@ -1,12 +1,12 @@
 CORE
 ../unreachable-instructions-basic-text/unreachable.c
 --unreachable-functions --json -
-"file name": ".*unreachable.c",
-"first line": 3,
+"file": ".*unreachable.c",
+"firstLine": 3,
 "function": "not_called",
-"last line": 6
+"lastLine": 6
 ^EXIT=0$
 ^SIGNAL=0$
 --
-"last line":[[:space:]]*$
+"lastLine":[[:space:]]*$
 ^warning: ignoring

src/goto-analyzer/unreachable_instructions.cpp

@@ -127,7 +127,7 @@ static void add_to_json(
 
   json_objectt entry{{"function", json_stringt(function_identifier)}};
   if(auto file_name_opt = file_name_string_opt(end_function->source_location))
-    entry["fileName"] = json_stringt{*file_name_opt};
+    entry["file"] = json_stringt{*file_name_opt};
 
   json_arrayt &dead_ins=entry["unreachableInstructions"].make_array();
 
@@ -270,11 +270,11 @@ static void json_output_function(
 {
   json_objectt entry{{"function", json_stringt(function)}};
   if(auto file_name_opt = file_name_string_opt(first_location))
-    entry["file name"] = json_stringt{*file_name_opt};
+    entry["file"] = json_stringt{*file_name_opt};
   if(auto line_opt = line_string_opt(first_location))
-    entry["first line"] = json_numbert{*line_opt};
+    entry["firstLine"] = json_numbert{*line_opt};
   if(auto line_opt = line_string_opt(last_location))
-    entry["last line"] = json_numbert{*line_opt};
+    entry["lastLine"] = json_numbert{*line_opt};
 
   dest.push_back(std::move(entry));
 }
@@ -289,11 +289,11 @@ static void xml_output_function(
 
   x.set_attribute("name", id2string(function));
   if(auto file_name_opt = file_name_string_opt(first_location))
-    x.set_attribute("file name", *file_name_opt);
+    x.set_attribute("file", *file_name_opt);
   if(auto line_opt = line_string_opt(first_location))
-    x.set_attribute("first line", *line_opt);
+    x.set_attribute("first_line", *line_opt);
   if(auto line_opt = line_string_opt(last_location))
-    x.set_attribute("last line", *line_opt);
+    x.set_attribute("last_line", *line_opt);
 }
 
 static void list_functions(