Finish converting existing comments for internal API docs (#8146)

* Finish converting existing comments for internal API docs

99% of this was just reformatting existing comments. Only two exceptions:

- Expanded upon `BuildResult::status` compat note

- Split up file-level `symbol-table.hh` doc comments to get
  per-definition docs

Also fixed a few whitespace goofs, turning leading tabs to spaces and
removing trailing spaces.

Picking up from #8133

* Fix two things from comments

* Use triple-backtick not indent for `dumpPath`

* Convert GNU-style `\`..'` quotes to markdown style in API docs

This will render correctly.

src/libutil/logging.hh

@@ -183,12 +183,17 @@ bool handleJSONLogMessage(const std::string & msg,
     const Activity & act, std::map<ActivityId, Activity> & activities,
     bool trusted);
 
-extern Verbosity verbosity; /* suppress msgs > this */
+/**
+ * suppress msgs > this
+ */
+extern Verbosity verbosity;
 
-/* Print a message with the standard ErrorInfo format.
-   In general, use these 'log' macros for reporting problems that may require user
-   intervention or that need more explanation.  Use the 'print' macros for more
-   lightweight status messages. */
+/**
+ * Print a message with the standard ErrorInfo format.
+ * In general, use these 'log' macros for reporting problems that may require user
+ * intervention or that need more explanation.  Use the 'print' macros for more
+ * lightweight status messages.
+ */
 #define logErrorInfo(level, errorInfo...) \
     do { \
         if ((level) <= nix::verbosity) {     \
@@ -199,9 +204,11 @@ extern Verbosity verbosity; /* suppress msgs > this */
 #define logError(errorInfo...) logErrorInfo(lvlError, errorInfo)
 #define logWarning(errorInfo...) logErrorInfo(lvlWarn, errorInfo)
 
-/* Print a string message if the current log level is at least the specified
-   level. Note that this has to be implemented as a macro to ensure that the
-   arguments are evaluated lazily. */
+/**
+ * Print a string message if the current log level is at least the specified
+ * level. Note that this has to be implemented as a macro to ensure that the
+ * arguments are evaluated lazily.
+ */
 #define printMsgUsing(loggerParam, level, args...) \
     do { \
         auto __lvl = level; \