[lldb-dap] Create a typescript extension for lldb-dap (#75515)

The main motivations behind this are two:

- Allow different companies developing their own vscode extensions for
LLDB to have a single contribution point, thus sharing resources and
working as a virtual large team.
- Allow for visual ways to configure the debugger, which currently has
to be done through launch.json files.

In terms of implementation, this is very straightforward and these are
the most important details:

- All the cpp code has been moved to a subfolder for cleanness. There's
a specific commit in the list of commits of this PR that just does that,
in case that helps reviewing this.
- A new folder `src-ts` has been created for the typescript code
- The ts extension can be used in two ways: as a regular vscode
extension and as a library. There file `extension.ts` explains which
entry point to use.
- The README has been updated the mention how to install the extension,
which is simpler than before. There are tw...