use remote cli when in remote terminal

[aeschli]

Fixes microsoft/vscode-remote-release#6625

Replaces #150131

This fix is for Linux/Mac only. On Linux, the shell login script adds /usr/local/bin to the front of the path. The Mac reorders the PATH segments, see #99878. On remote systems that also have desktop code installed, this causes the desktop code shell script to be found before the remote cli code script.

The fix is to have the Desktop code / code-insiders shell script detect if it is invoked in a remote terminal and forward he call the remote cli command

• To detect if we are in a remote terminal we use the VSCODE_IPC_HOOK_CLI env variable.
• To find the remote cli, we look in the PATH if a second code command is found under a path remote-cli

On Windows, the remote code command is always first.

[aeschli]

I also update the code command for linux to use @@APPNAME@@ instead of @@NAME@@. That makes clear what name really stands for product.applicationName. That is also consistent with the naming in the scripts for the other platforms