Upgrader: handle missing obsolete extensions

[colemanw]

Overview

This improves the mechanism for auto-disabling obsolete extensions during the upgrade process to disable extensions even if they are missing.

Before

Obsolete extensions not disabled if missing.

After

Obsolete extensions disabled even if missing.

Comments

This came up while testing upgrade to 5.19 which includes Api v4. See #15309

[civibot]

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[seamuslee001]

(CiviCRM Review Template WORD-1.2)

• General standards
  • (r-explain) Pass
  • (r-user) Pass
  • (r-doc) Pass
  • (r-run) Pass I replicated my steps from Migrate APIv4 into civicrm-core #15309 (comment) and confirmed that with this patch applied the api4 extension is correctly disabled no missing module notices show and apiv4 explorer works first time as expected
• Developer standards
  • (r-tech) Pass
  • (r-code) Pass
  • (r-maint) Pass
  • (r-test) Pass

[seamuslee001]

Test fails are unrelated merging