New Method Logger.logDatabaseErrors()

Resolve #295 by adding a new method Logger.logDatabaseErrors(), including several overloads for using LogMessage/String, as well as the different database result classes. When this method is called, if the list of database results includes 1 or more errors (based on isSuccess() == false), then a new log entry is added, and the JSON of any unsuccessful database results is serialized/stored in the log entry.

The full list of method overloads is:

global static LogEntryEventBuilder logDatabaseErrors(LoggingLevel loggingLevel, LogMessage logMessage, List<Database.DeleteResult> deleteResults);
global static LogEntryEventBuilder logDatabaseErrors(LoggingLevel loggingLevel, String message, List<Database.DeleteResult> deleteResults);
global static LogEntryEventBuilder logDatabaseErrors(LoggingLevel loggingLevel, LogMessage logMessage, List<Database.MergeResult> mergeResults);
global static LogEntryEventBuilder logDatabaseErrors(LoggingLevel loggingLevel, String message, List<Database.MergeResult> mergeResults);
global static LogEntryEventBuilder logDatabaseErrors(LoggingLevel loggingLevel, LogMessage logMessage, List<Database.SaveResult> saveResults);
global static LogEntryEventBuilder logDatabaseErrors(LoggingLevel loggingLevel, String message, List<Database.SaveResult> saveResults);
global static LogEntryEventBuilder logDatabaseErrors(LoggingLevel loggingLevel, LogMessage logMessage, List<Database.UpsertResult> upsertResults);
global static LogEntryEventBuilder logDatabaseErrors(LoggingLevel loggingLevel, String message, List<Database.UpsertResult> upsertResults);
global static LogEntryEventBuilder logDatabaseErrors(LoggingLevel loggingLevel, LogMessage logMessage, List<Database.UndeleteResult> undeleteResults);
global static LogEntryEventBuilder logDatabaseErrors(LoggingLevel loggingLevel, String message, List<Database.UndeleteResult> undeleteResults);

Thanks to @jamessimone for the great suggestion & code review!