fix(langchain,langchain-classic): update model provider classes for Azure AI Foundry (#35812)

Fixes #35811

Updates support for the "azure_ai" provider in both chat model and
embeddings initialization, ensuring consistency across the codebase and
removing the use of deprecated classes `AzureAIChatCompletionsModel` and
`AzureAIEmbeddingsModel`. The changes primarily involve updating
provider mappings and instantiation logic for Azure AI integrations.

**Changes:**

* Updated the chat model initialization logic in `langchain_classic` and
`langchain_v1` to use `AzureAIOpenAIApiChatModel` instead of the
deprecated `AzureAIChatCompletionsModel` for the "azure_ai" provider.
[[1]](diffhunk://#diff-969731928b9d70dac2677539a711478df103ce70024b4c61e95bd7b584bb841dL395-R398)
[[2]](diffhunk://#diff-31b725e3fe9b2f92342af5cda9bf6e61c4bc0b69efd8c25743269f45c52571b2L41-R41)
* Added support for the "azure_ai" provider in embeddings
initialization, mapping it to the new `AzureAIOpenAIApiEmbeddingsModel`
class in both `langchain_classic` and `langchain_v1`.
[[1]](diffhunk://#diff-9490c8d3daa7c5b66d10ce2961f2bc1a6a35005150125c905316adb728bf80d6R9)
[[2]](diffhunk://#diff-9490c8d3daa7c5b66d10ce2961f2bc1a6a35005150125c905316adb728bf80d6R209-R212)
[[3]](diffhunk://#diff-d37aa14c07863cc184800713b88a9c25fdb43efd1a4daa31df3ecabb2f70f177R16)

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Co-authored-by: Mason Daugherty <[email protected]>
Co-authored-by: Mason Daugherty <[email protected]>