tp: implement CREATE_FUNCTION SQL function

This allows defining functions directly from SQL. This will make writing
reusable snippets of code a lot more lightweight.

Change-Id: If6207fac3815b9b584da9648a0fdc525f2f63670
Bug: 190219056
diff --git a/BUILD b/BUILD
index fc4ffa9..241626b 100644
--- a/BUILD
+++ b/BUILD
@@ -1153,6 +1153,8 @@
 perfetto_filegroup(
     name = "src_trace_processor_sqlite_sqlite",
     srcs = [
+        "src/trace_processor/sqlite/create_function.cc",
+        "src/trace_processor/sqlite/create_function.h",
         "src/trace_processor/sqlite/db_sqlite_table.cc",
         "src/trace_processor/sqlite/db_sqlite_table.h",
         "src/trace_processor/sqlite/query_cache.h",