refactor: remove rangeStrategy=pin from versioning modules

[rarkins]

Changes

Refactors getNewValue logic to replace it with an optional getPinnedValue() where rangeStrategy=pin. This way each versioning module doesn't need to add and test extensive "pin" logic.

Context

Refactor prior to restoring pinVersions logic.

Documentation (please check one with an [x])

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• No documentation update is required

How I've tested my work (please select one)

I have verified these changes via:

• Code inspection only, or
• Newly added/modified unit tests, or
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• Both unit tests + ran on a real repository

[rarkins]

I noticed something curious: with go.mod values, it's impossible to pin to a version, so I was wondering how rangeStrategy=pin worked for it. Turns out we use semver versioning so everything looks like an exact version already and doesn't need pinning.

[viceice]

LGTM beside the open question

[rarkins]

Let's merge in v42