chore: Switch SAST scanning to semgrep

Description

Switches SAST scanners to semgrep, see https://docs.gitlab.com/ee/user/application_security/sast/analyzers.html#activate-semgrep-based-scanning for analyzer cleanup and deprecations.

This change unifies findings behind the future-proof semgrep scanner instead

Related Issue

Relates to #1003 (closed)

How Has This Been Tested?

See https://gitlab.com/gitlab-org/cli/-/pipelines/556802599

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation
• Chore (Related to CI or Packaging to platforms)