feat(no-misused-observables): improve report loc for methods

[JasonWeinzierl]

See tseslint issue 10216. If a property is a function, instead of reporting the entire function, report either its return type or else use getFunctionHeadLocation to report a more narrow location. See tests for example.

[github-actions]

LCOV of commit b563b7d during .github/workflows/ci.yml #604

Summary coverage rate:
  lines......: 96.7% (4474 of 4628 lines)
  functions..: 96.2% (275 of 286 functions)
  branches...: no data found

Files changed coverage rate:
                                                                    |Lines       |Functions  |Branches    
  Filename                                                          |Rate     Num|Rate    Num|Rate     Num
  ========================================================================================================
  src/rules/no-misused-observables.ts                               | 4.1%    438| 0.0%    18|    -      0