Fix code-coverage reports for ts/tsx

[zinserjan]

This PR applys sourcemaps for code-coverage reports.

Before:

--------------------------|----------|----------|----------|----------|----------------|
File                      |  % Stmts | % Branch |  % Funcs |  % Lines |Uncovered Lines |
--------------------------|----------|----------|----------|----------|----------------|
All files                 |    34.69 |    30.77 |     37.5 |    36.17 |                |
 App.tsx                  |    80.95 |    57.14 |       75 |    89.47 |            4,5 |
 index.tsx                |        0 |      100 |      100 |        0 |2,3,4,5,6,7,8,9 |
 registerServiceWorker.ts |        0 |        0 |        0 |        0 |... 49,50,51,55 |
--------------------------|----------|----------|----------|----------|----------------|

After:

--------------------------|----------|----------|----------|----------|----------------|
File                      |  % Stmts | % Branch |  % Funcs |  % Lines |Uncovered Lines |
--------------------------|----------|----------|----------|----------|----------------|
All files                 |    24.32 |        0 |       20 |    22.22 |                |
 App.tsx                  |      100 |      100 |      100 |      100 |                |
 index.tsx                |        0 |      100 |      100 |        0 |2,3,4,5,6,7,8,9 |
 registerServiceWorker.ts |        0 |        0 |        0 |        0 |... 49,50,51,55 |
--------------------------|----------|----------|----------|----------|----------------|

[ChristopherHoffman]

This fix would be highly appreciated. You never realized how just helpful the code coverage reports are until they give you wrong information, and you have to track down uncovered code yourself.

[wmonk]

@zinserjan can you fix this conflict please 😄

[zinserjan]

@wmonk done