log: use std::source_location in place of __func__, __FILE__, __LINE__

The std::source_location conveniently stores the file name, line number,
and function name of a source code location. We switch to using it instead
of the __func__ identifier and the __FILE__ and __LINE__ macros.

BufferedLog is changed to have a std::source_location member, replacing the
source_file, source_line, and logging_function members. As a result,
MemUsage no longer explicitly counts source_file or logging_function as the
std::source_location memory usage is included in the MallocUsage call.

This also changes the behavior of -logsourcelocations as std::source_location
includes the entire function signature. Because of this, the functional test
feature_config_args.py must be changed to no longer include the function
signature as the function signature can differ across platforms.

Co-Authored-By: Niklas Gogge <n.goeggi@gmail.com>
Co-Authored-By: stickies-v <stickies-v@protonmail.com>

test/functional/feature_config_args.py

@@ -82,7 +82,7 @@ class ConfArgsTest(BitcoinTestFramework):
 
         self.log.debug('Verifying that disabling of the config file means garbage inside of it does ' \
             'not prevent the node from starting, and message about existing config file is logged')
-        ignored_file_message = [f'[InitConfig] Data directory "{self.nodes[0].datadir_path}" contains a "bitcoin.conf" file which is explicitly ignored using -noconf.']
+        ignored_file_message = [f'Data directory "{self.nodes[0].datadir_path}" contains a "bitcoin.conf" file which is explicitly ignored using -noconf.']
         with self.nodes[0].assert_debug_log(timeout=60, expected_msgs=ignored_file_message):
             self.start_node(0, extra_args=settings + ['-noconf'])
         self.stop_node(0)