Add TypeScript client check in the CI
This MR sets :
- disables tsc checks for JS files (the checks will be done only for ts/tsx files)
- noImplicitAny = true for TS/TSX files
- fixes errors raised by tsc (details are in commit messages)
- include the TSC checks in the CI allowing to prevent regressions.
There is also a bug fix of a bug introduced by !1343 (merged).