[Request] Add support for installing dependencies in the extest install-vsix command

[priyamsahoo]

Description:

The automatic building of the extension is not proper in certain cases due to vsce linking bugs. To work around this issue, we generate our own .vsix file and run extest install-vsix before running the actual ui tests.

However, our extension has dependencies on other extensions, and there is no option to install dependencies in the extest install-vsix command, although the --install_dependencies arg is present in extest setup-tests. Thus, to overcome this, we need to use an additional command, extest install-from-marketplace, to install the dependencies before running the tests. This creates a long chain of dependencies, resulting in a complicated testing script.

Eg:

"test-ui": "extest get-vscode -c 1.71.0 -s out/test-resources && extest get-chromedriver -s out/test-resources && extest install-vsix -f custom-built.vsix -e out/ext -s out/test-resources && extest install-from-marketplace dependent.extension.1 dependent.extension.2 -e out/ext -s out/test-resources && extest run-tests -s out/test-resources -e out/ext --code_settings test/testFixtures/settings.json out/client/test/ui-test/allTestsSuite.js"

Proposal:

1. Add --install_dependencies arg to the extest install-vsix command. This will allow for the installation of dependencies without having to run another command for it.
2. Alternately, add a new arg to the extest setup-tests and extest setup-and-run command that allows for custom scripts to build the extension before installing.