refactor: simplify electron mirror management

[karanbirsingh]

Description of changes

Currently updating the electron version also requires some changes to build pipeline variables because the mirror URL needs to change (see #2538). This PR leverages improvements in @electron/get 1.12.2 to simplify this process so that only updating the asset number is required (moved to YAML) - the rest of the URL is computed from package.json and constant ADO variables.

Before this PR is merged, I need to add the constant ADO variables to the pipeline. So far they were added on a trial run you can see here.

Pull request checklist

• Addresses an existing issue: #0000
• Ran yarn fastpass
• Added/updated relevant unit test(s) (and ran yarn test)
• Verified code coverage for the changes made. Check coverage report at: <rootDir>/test-results/unit/coverage
• PR title AND final merge commit title both start with a semantic tag (fix:, chore:, feat(feature-name):, refactor:). See CONTRIBUTING.md.
• (UI changes only) Added screenshots/GIFs to description above
• (UI changes only) Verified usability with NVDA/JAWS