feat: Extract component description from aria-describedby

[gethinwebster]

Description

Adds a description field to the component metadata tree output. The description is extracted by resolving aria-describedby on the same element used for label resolution (found via the component's label selector). All space-separated IDs are resolved and their text content concatenated, matching screen reader behavior.

This works because aria-labelledby and aria-describedby are always placed on the same interactive control element in Cloudscape components. FormField is correctly excluded since its label selector points to a <label> element which does not have aria-describedby.

Example output

For an Input inside a FormField with constraintText="Must be 3-20 characters":

{
  "name": "awsui.Input",
  "label": "Username",
  "description": "Must be 3-20 characters",
  "properties": { "value": "..." }
}

Changes

• Added description?: string to GeneratedAnalyticsMetadataComponentTree interface
• Added resolveComponentDescription helper that uses the label selector to find the element, checks aria-describedby, and concatenates all referenced IDs' text content. Iterates through array selectors (like label resolution) returning the first match.
• Integrated into processMetadata: description is extracted when a component has name and a label selector defined
• 7 new unit tests covering: basic extraction, multi-ID concatenation, no describedby, no label selector, label element without describedby, missing IDs, array selector fallback

Testing

All 412 unit tests pass.

Components unit tests in dry run expected to fail because 1) of as-yet in-pipeline diffs from a previous PR, 2) expected diffs from this PR (description now provided in some of the test cases)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.99%. Comparing base (eb4fa98) to head (fae39d1).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #220      +/-   ##
==========================================
+ Coverage   98.97%   98.99%   +0.01%     
==========================================
  Files          44       44              
  Lines        1272     1293      +21     
  Branches      351      337      -14     
==========================================
+ Hits         1259     1280      +21     
- Misses         12       13       +1     
+ Partials        1        0       -1     

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