feat: use permalinks in Copy Link to Active File command

Related to #699 (closed)

This MR changes the behaviour of Copy Link to Active File command.

Instead of using the branch name in the link, we include the SHA of the last commit that changed the file — effectively making the link always a permalink.

- https://gitlab.com/gitlab-org/gitlab-web-ide-vscode-fork/blob/main/src/vs/platform/files/node/diskFileSystemProviderServer.ts#L27
+ https://gitlab.com/gitlab-org/gitlab-web-ide-vscode-fork/-/blob/53584f7630d0dfac5eaba023029e4c5ab820e78f/src/vs/platform/files/node/diskFileSystemProviderServer.ts#L27

copy-link-permalink

This change also affects the Open Active File on GitLab since these commands share the same logic.

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This MR was produced in four pairing sessions as a part of initiative to increase the number of maintainers in this project: Extend Maintainers (#656 - closed)

• Adding a feature to GitLab Workflow VS Code Extension - Session 1 - YouTube
• Adding a feature to GitLab Workflow VS Code Extension - Session 2 - YouTube
• Adding a feature to GitLab Workflow VS Code Extension - Session 3 - YouTube
• Adding a feature to GitLab Workflow VS Code Extension - Session 4 - YouTube

You can see how it's been developed.