feat(codegen): strip HTML tags from documentation traits in generated JSDoc

[TrevorBurnham]

Issue #, if available:

Resolves aws/aws-sdk-js-v3#6876

Description of changes:

Smithy model @documentation trait values often contain raw HTML markup (<p>, <a href="...">, <code>, <ul>/<li>, etc.). The TypeScript codegen currently passes this HTML through verbatim into JSDoc comments, making hover docs in editors like VS Code and Neovim very hard to read.

For example, generated code ends up with comments like:

<p>Registers a new task definition from the supplied <code>family</code> and
<code>containerDefinitions</code>. For more information, see
<a href="https://docs.aws.amazon.com/...">Amazon ECS Task Definitions</a>
in the <i>Amazon Elastic Container Service Developer Guide</i>.</p>

After this change, the same ECS example renders as:

Registers a new task definition from the supplied `family` and
`containerDefinitions`. For more information, see Amazon ECS Task Definitions
in the Amazon Elastic Container Service Developer Guide.

Implementation details

Added a DocumentationConverter utility class in smithy-typescript-codegen with an htmlToPlainText(String html) method that converts HTML documentation into clean plaintext suitable for JSDoc. The converter:

• Extracts link text from <a> tags (drops URLs)
• Wraps <code>/<pre> content in backticks
• Converts <li> items to dash-prefixed lines
• Converts <dt>/<dd> definition list elements to readable format
• Replaces block-level elements (<p>, <br>, <h1>–<h6>, <div>, etc.) with paragraph breaks
• Strips all remaining inline formatting tags (<b>, <i>, <strong>, <em>, <span>, etc.)
• Decodes HTML entities (&, <, >, ", ',  , numeric/hex entities)
• Normalizes whitespace (collapses runs of blank lines and spaces)

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