fix(spec): inherit path-level parameters for cross-file $ref path items

[yogeshwaran-c]

What kind of change does this PR introduce?

Bug fix.

What is the current behavior?

Path-level (a.k.a. "global") parameters declared on an OpenAPI path
item are not propagated to operations under that path when the path
item is reached through a cross-file $ref.

Reproduction (from issue):

• openapi.yaml references a path from an external file:

  paths:
    /pets/{petId}:
      $ref: ./petstore.yaml#/paths/~1pets~1{petId}

• petstore.yaml defines the path item with a path-level
  parameters array plus get and options operations.
• The options operation declares no parameters of its own.

When the spec is loaded via openapi.yaml, the options operation
renders with the path-level parameter missing. When the same spec is
loaded directly via petstore.yaml, both operations correctly show
the parameter.

Closes #5667.

Root cause

swagger-client's generic normalize step
(resolver/strategies/generic/normalize.js) copies path-level
parameters into each operation under that path. swagger-ui depends on
this inheritance — operations are rendered using the operation-level
parameters array only.

When a path item is dereferenced from another file, swagger-ui lazily
resolves the subtree at ["paths", "/<path>"] via the
requestResolvedSubtree machinery in src/core/plugins/spec/actions.js.
The subtree resolver runs normalize against the root spec, but at
that point the root spec still has only { $ref: ... } at the path
position — there are no operations and no parameters to inherit
from. For OAS 3.0 the post-resolve normalize pass is skipped
(subtree-resolver/index.js passes skipNormalization: !isOpenAPI31),
so the inheritance never runs against the dereferenced output.

Fix

After a batch of subtrees is resolved, walk the resolved
paths object and, for each path item that has path-level
parameters, push those parameters into every operation that is
missing them. The merge is idempotent and uses the same duplicate
detection as swagger-client (matching by name, $ref, or $$ref),
so non-$ref'd paths already normalized by swagger-client are left
untouched.

What is the new behavior?

For both $ref'd and inline path items, path-level parameters appear
on every operation under that path. Existing operation-level
parameters take precedence (no duplicates created).

How Has This Been Tested?

• New Jest unit tests in
  test/unit/core/plugins/spec/path-item-parameters.js covering:
  inherit when missing, no duplicates by name, no duplicates by $ref,
  no-op when path item has no parameters, ignore non-operation keys
  (summary, description, servers), create operation parameter
  array when missing.
• New Cypress e2e test in test/e2e-cypress/e2e/bugs/5667.cy.js using
  a two-file fixture (5667-root.yaml, 5667-pets.yaml) that
  reproduces the issue exactly as reported. The tests fail without
  the fix (confirmed by reverting the fix and re-running) and pass
  with it.
• Verified the surrounding spec-plugin unit suites
  (actions, selectors, reducer) still pass.

Additional context

The new helper lives at src/core/plugins/spec/path-item-parameters.js
and is intentionally scoped to JS-side plain-object manipulation so it
can run on the mutable resultMap accumulator produced by
debResolveSubtrees in
src/core/plugins/spec/actions.js. No other call sites are touched.