uorb: compress format definitions

Reduces flash usage by ~16KB.

- compress formats at build-time into a single string with all formats
- then at runtime iteratively decompress using
  https://github.com/atomicobject/heatshrink

Tools/msg/templates/uorb/msg.json.em

@@ -0,0 +1,49 @@
+@###############################################
+@#
+@# PX4 ROS compatible message source code
+@# generation for C++
+@#
+@# EmPy template for generating <msg>.h files
+@# Based on the original template for ROS
+@#
+@###############################################
+@# Start of Template
+@#
+@# Context:
+@#  - file_name_in (String) Source file
+@#  - spec (msggen.MsgSpec) Parsed specification of the .msg file
+@#  - search_path (dict) search paths for genmsg
+@#  - topics (List of String) topic names
+@#  - all_topics (List of String) all generated topic names (sorted)
+@###############################################
+
+@{
+import genmsg.msgs
+import json
+
+from px_generate_uorb_topic_helper import * # this is in Tools/
+
+uorb_struct = '%s_s'%name_snake_case
+
+sorted_fields = sorted(spec.parsed_fields(), key=sizeof_field_type, reverse=True)
+struct_size, padding_end_size = add_padding_bytes(sorted_fields, search_path)
+topic_fields = ["%s %s" % (convert_type(field.type, True), field.name) for field in sorted_fields]
+
+dependencies = []
+for field in spec.parsed_fields():
+    if not field.is_header:
+        type_name = field.type
+        # detect embedded types
+        sl_pos = type_name.find('/')
+        if sl_pos >= 0: # nested type
+            dependencies.append(field.base_type)
+}@
+
+{
+@# join all msg files in one line e.g: "float[3] position;float[3] velocity;bool armed;"
+		"fields": @( json.dumps(bytearray(";".join(topic_fields)+";", 'utf-8').decode('unicode_escape')) ),
+		"orb_ids": @( json.dumps([ all_topics.index(topic) for topic in topics]) ),
+		"main_orb_id": @( all_topics.index(name_snake_case) if name_snake_case in all_topics else -1 ),
+		"dependencies": @( json.dumps(list(set(dependencies))) ),
+		"name": "@( spec.full_name )"
+}