tsconfig: Disable strictNullChecks

The conversion done in the previous commits came with hundreds of
violations of this rule. While this could be addressed by better types,
it will take some work and can be deferred. A new issue/PR will be
created after this is merged.

<#1864 (comment)>

tsconfig.json

@@ -32,6 +32,7 @@ Visit https://aka.ms/tsconfig.json for a detailed list of options.
 
     /* Type Checking */
     "strict": true,                                      /* Enable all strict type-checking options. */
+    "strictNullChecks": false,                           /* Allow unhandled false/null/undefined values to make incremental TypeScript adoption easier. */
     "noImplicitAny": false,                              /* Allow implicit any to make incremental TypeScript adoption easier. */
     "noUnusedLocals": true,                              /* Enable error reporting when a local variables aren't read. */
     "noUnusedParameters": true,                          /* Raise an error when a function parameter isn't read */