Add support for Debugging on Alpine

[WardenGnaw]

• @gregg-miskelly

This enables Debug Launch/Attach for Linux-x64 Alpine.

Addresses debugging scenario for #4827

Added notes via TODO(LS-alpine) when Language Service has alpine support so we can have a full activation instead of a debugger only version.

Tested using remote-container with the following configurations:

Dockerfile

FROM mcr.microsoft.com/vscode/devcontainers/base:dev-alpine-3.14

RUN apk add --no-cache gdb file g++ clang coreutils

devcontainer.json

{
	"name": "Alpine",
	"build": {
		"dockerfile": "Dockerfile",
		// Update 'VARIANT' to pick an Alpine version: 3.11, 3.12, 3.13, 3.14
		"args": { "VARIANT": "3.14" }
	},
	
	// Set *default* container specific settings.json values on container create. 
	"settings": {},

	// Add the IDs of extensions you want installed when the container is created.
	// Note that some extensions may not work in Alpine Linux. See https://aka.ms/vscode-remote/linux.
	"extensions": [
		"ms-vscode.cpptools"
	],

	// Use 'forwardPorts' to make a list of ports inside the container available locally.
	// "forwardPorts": [],

	// Use 'postCreateCommand' to run commands after the container is created.
	// "postCreateCommand": "uname -a",

	// Uncomment when using a ptrace-based debugger like C++, Go, and Rust
	// "runArgs": [ "--cap-add=SYS_PTRACE", "--security-opt", "seccomp=unconfined" ],

	// Comment out connect as root instead. More info: https://aka.ms/vscode-remote/containers/non-root.
	"remoteUser": "vscode"
}

[WardenGnaw]

Also a huge thanks to @Trass3r for the help and validation for this scenario.

[bobbrow]

functions should be named like isAlpine

[bobbrow]

Do we want one? What would it take for us to make it work? It would be better if we could just support the platform across the board.

[WardenGnaw]

Lets discuss this in our next meeting.

[Trass3r]

Well the current one is glibc-based.

[Trass3r]

Any updates?

[WardenGnaw]

@Trass3r We are planning on fully adding Alpine support for both the Language Service and Debugger.

The current plan is targeted for 1.8.0.

[Trass3r]

I see. But that will take a while.
In the meantime couldn't it "simply" be changed to reference the correct debugger package so these steps become unnecessary?

[WardenGnaw]

The activation of the extension depends on a bunch of the checks I added to disable the Language Service.
See // TODO(LS-alpine) in the changes.

The simple change is to fix the download for alpine machines since we download the linux-x64 one based on the logic in download packages.

export function PlatformsMatch(value: IPackage, info: PlatformInformation): boolean {
    if (IsAlpine()) {
        // Alpine needs to be explicitly stated in packages list in order to be downloaded.
        return value.platforms && value.platforms.indexOf("alpine-linux") !== -1;
    }

    return !value.platforms || value.platforms.indexOf(info.platform) !== -1;
}

[Colengms]

@WardenGnaw Can this PR be abandoned, now that we support Alpine x64?

[WardenGnaw]

Closing in favor for 1.8.0-insiders3