Fix discriminator model lookup when used together with model name suffix

[hrach]

When modelNamePrefix or modelNameSuffix is configured, MappedModel.modelName stores the transformed name (e.g. AppleReqDiscDto), while the allProcessedModels map in postProcessAllModels is keyed by the raw OAS schema name (e.g. AppleReqDisc). This mismatch caused ModelUtils.getModelByName to return null, leaving
MappedModel.model unresolved — breaking discriminator-based serialization in generated code.

The fix adds a schemaName field to CodegenDiscriminator.MappedModel that preserves the original OAS schema name before any prefix/suffix transformation. During postProcessAllModels, the lookup now uses schemaName (falling back to modelName for backward compatibility), enabling a direct O(1) map key hit instead of
requiring a linear scan.

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No issues found across 3 files

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[hrach]

Hi @wing328, I saw you reviewed similar things around the discriminator. Could you please review this one? :) thx.

[wing328]

thanks for the fix

let's give it a try

[hrach]

thank you :)