[NFC] Inject asSwiftSafeName as a dependency

[czechboy0]

Motivation

Arguably, we should have done this before, but here we go. In order to allow dynamically customizing the logic for converting OpenAPI to Swift identifiers (in support of staging SOAR-0001 gradually), we need to dependency-inject the (String) -> String function to all the places that need to do this conversion.

Modifications

This PR doesn't change any behavior (NFC - no functional change), it just refactors the code to have a single funnel point through which all the conversion goes, which has access to the Config and can inspect feature flags.

Right now, the default behavior is still the same, but this PR creates room for adding the alternative logic from SOAR-0001.

Result

NFC, prepares room for a subsequent PR.

Now it's possible to conditionalize the Swift name computing logic based on feature flags.

Test Plan

All tests are passing, adapted as needed, created conveniences in tests for getting a default Config, but also made it possible to test the logic by explicitly passing the feature flag.

[czechboy0]

FYI, @denil-ct, once this lands, you'll be able to add your logic here and then test is by providing the feature flag proposal0001.

[simonjbeaumont]

I don't think we should be mixing in the injected function with the description types.

Either the names we compute within them should be safed by the thing that constructs them, or the computed properties should be made functions that take a safer, or they should return unsafed names, which the caller then safes.

I think in this way, we might preserve some better layering? WDYT?