CMake: Add custom Dev build type.

Introduce new build type Dev that replaces RelWithDebInfo for development
builds off master and has optimizations, debug info, and logging enabled.
Keep assertions enabled for RelWithDebInfo.

contrib/local.mk.example

@@ -13,16 +13,19 @@
 
 # Sets the build type; defaults to Debug. Valid values:
 #
-# - Debug:          Disables optimizations (-O0), enables debug information.
+# - Debug:          Disables optimizations (-O0), enables debug information and logging.
 #
-# - RelWithDebInfo: Enables all optimizations that do not interfere with
+# - Dev:            Enables all optimizations that do not interfere with
 #                   debugging (-Og if available, -O2 and -g if not).
-#                   Enables debug information.
+#                   Enables debug information and logging.
+#
+# - RelWithDebInfo: Enables optimizations (-O2) and debug information.
+#                   Disables logging.
 #
 # - MinSizeRel:     Enables all -O2 optimization that do not typically
 #                   increase code size, and performs further optimizations
 #                   designed to reduce code size (-Os).
-#                   Disables debug information.
+#                   Disables debug information and logging.
 #
 # - Release:        Same as RelWithDebInfo, but disables debug information.
 #