Update Newtonsoft.Json to 13.0.3, adjust code for nullability #2811

Job	Run time
Build all projects without errors	11m 52s
JS unit tests	1m 10s
.NET unit tests (ubuntu-latest)	3m 5s
Build published projects without warnings (Release)	2m 56s
.NET unit tests (windows-2022)	12m 31s
Build published projects without warnings (Debug)	3m 27s
UI tests (chrome, ubuntu-latest, Production, Default)	13m 7s
.NET unit tests (macOS-latest)	8m 25s
UI tests (chrome, windows-2022, Development, Default)	25m 57s
UI tests (firefox, ubuntu-latest, Development, Default)	17m 43s
UI tests (firefox, ubuntu-latest, Production, Default)	17m 6s
UI tests (firefox, ubuntu-latest, Development, ExperimentalFeaturesTests)	18m 42s
UI tests (chrome, ubuntu-latest, Production, ExperimentalFeaturesTests)	13m 16s
	2h 29m 17s

Provide feedback