Replace periods with underscores in Rust model names

[ekarcnevets]

Fix issue where period-delimited model names (e.g. microsoft.graph.fido2AuthenticationMethod) were being converted to unwieldy names with "Period" substitutions. Now periods are replaced with underscores like hyphens, resulting in cleaner and more idiomatic Rust identifiers.

@frol @farcaller @richardwhiuk @paladinzh @jacob-pro

Fixes #15254

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[ekarcnevets]

unsure if this should be targeting 8.0.x since it changes model names?

[wing328]

thanks for the PR

we will consider this as a bug fix as other generators are using similar naming convention.

if users need a way to rollback or customize the model name in whatever way they want, they can use the model name mpaping option: https://github.com/openapitools/openapi-generator/blob/master/docs/customization.md#name-mapping

[wing328]

@ekarcnevets thanks again for the PR which has been merged.

When you've time, can you please PM me via Slack for a few quick questions?

https://join.slack.com/t/openapi-generator/shared_invite/zt-36ucx4ybl-jYrN6euoYn6zxXNZdldoZA