[Internal] VectorEmbeddingPolicy: Adds EmbeddingSource block to Embedding model

[aavasthy]

Pull Request Template

Description

Adds EmbeddingSource block to entries in VectorEmbeddingPolicy, describing where the SDK should call the embedding service for a given vector path — including the source document paths to
embed, the model and deployment name, the service endpoint, and the authentication type (ApiKey or Entra)

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)

Closing issues

To automatically close an issue: closes #5840

[ananth7592]

LGTM

[kushagraThapar]

Changelog entry is missing, let's add it.

[aayush3011]

LGTM

[ananth7592]

LGTM

[kushagraThapar]

1. EmbeddingSource has no Equals/GetHashCode, but Embedding.Equals uses object.Equals on it

&& object.Equals(this.EmbeddingSource, that.EmbeddingSource);

Since EmbeddingSource doesn't override Equals, this is reference equality. Two Embedding instances with semantically-identical EmbeddingSource blocks
(different objects) will compare as not-equal. Either implement IEquatable on the new sealed class, or compare field-by-field in
Embedding.Equals.

2. Silent pre-existing bug fix in Embedding.Equals — behavior change, undocumented On main, Equals had this.Dimensions.Equals(that.Dimensions) (comparing
   Dimensions twice). This PR changes it to this.DistanceFunction.Equals(that.DistanceFunction). Good catch — but previously two embeddings differing only in
   DistanceFunction were considered equal; now they're not. Should be called out in the PR description / changelog so it's not silently shipped.

[aavasthy]

1. EmbeddingSource has no Equals/GetHashCode, but Embedding.Equals uses object.Equals on it

&& object.Equals(this.EmbeddingSource, that.EmbeddingSource);

Since EmbeddingSource doesn't override Equals, this is reference equality. Two Embedding instances with semantically-identical EmbeddingSource blocks (different objects) will compare as not-equal. Either implement IEquatable on the new sealed class, or compare field-by-field in Embedding.Equals.

2. Silent pre-existing bug fix in Embedding.Equals — behavior change, undocumented On main, Equals had this.Dimensions.Equals(that.Dimensions) (comparing
   Dimensions twice). This PR changes it to this.DistanceFunction.Equals(that.DistanceFunction). Good catch — but previously two embeddings differing only in
   DistanceFunction were considered equal; now they're not. Should be called out in the PR description / changelog so it's not silently shipped.

Fixed in the latest commit. EmbeddingSource now implements IEquatable with field-by-field Equals and GetHashCode (referenced from here https://msdata.visualstudio.com/CosmosDB/_git/CosmosDB?path=/Product/Microsoft.Azure.Documents/SharedFiles/EmbeddingSource.cs&version=GBmaster&line=145&lineEnd=146&lineStartColumn=1&lineEndColumn=1&lineStyle=plain&_a=contents).

On the DistanceFunction fix: keeping it in this PR since Embedding.Equals had to change here anyway to fold in the new EmbeddingSource field.

[kushagraThapar]

LGTM, thanks @aavasthy