Issue #3580405: Deprecate renderEmbedCode() in 3.1.0

Frank Mablyrequested to merge
issue/video_embed_field-3580405:3580405-deprecate-renderembedcode-in into 3.x

Add @deprecated annotation and @trigger_error() to renderEmbedCode() in ProviderPluginInterface, ProviderPluginBase, and all provider plugins. Update tests to use renderEmbed() instead.

Closes #3580405

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