Random doc updates

[gewarren]

Follow up to dotnet/ml-api-docs#175 and other grammar improvements.

So we can do the best job, please check:

• There's a descriptive title that will make sense to other developers some time from now.
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• Your change description explains what the change does, why you chose your approach, and anything else that reviewers should know.
• You have included any necessary tests in the same PR.

[Copilot]

Pull Request Overview

This PR refines XML documentation across several text and transformer components, improving grammar, clarity, and example references.

• Standardizes summary and <param> XML tags to use action verbs (e.g., “Creates”, “Gets or sets”).
• Improves phrasing and adds <remarks> and explicit <see> links for usage examples.
• Corrects hyphenation and list punctuation in descriptions.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/Microsoft.ML.Transforms.Text/TextFeaturizingEstimator.cs	Refined XML comments: grammar fixes, added <remarks> and <see> links
src/Microsoft.ML.Transforms/CustomMappingTransformer.cs	Enhanced <param> descriptions for better clarity
src/Microsoft.ML.Transforms/CategoricalCatalog.cs	Standardized summary XML to use action verbs

Comments suppressed due to low confidence (1)

src/Microsoft.ML.Transforms.Text/TextFeaturizingEstimator.cs:213

• Since Norm is a public field that can be assigned, consider updating the summary to "Gets or sets the norm of the output vector. It will be normalized to one." to accurately reflect its mutability.

Gets the norm of the output vector. It will be normalized to one.