fix: avoid variable shadowing in generated operation code

[timovv]

Copilot PR

Problem

When a TypeSpec operation has a parameter whose name collides with a local variable in the generated code, the emitter produces code with a Cannot redeclare compilation error.

For example, a @path parameter named path causes:

export function _getResultFileSend(
  context: Client,
  operationId: string,
  path: string,                         // function parameter
  options: GetResultFileOptionalParams = { requestOptions: {} },
): StreamableMethod {
  const path = expandUrlTemplate(       // ERROR: Cannot redeclare 'path'
    ...
  );

The same class of bug could also occur with parameters named result, headers, payload, or streamableMethod in getOperationFunction.

Fix

• Extract the private generateLocallyUniqueName() helper from Binder into namingHelpers.ts so it can be reused across the codebase, and update Binder to import it.
• In getSendPrivateFunction: use generateLocallyUniqueName("path", paramNames) so the local variable is renamed to path_1 (etc.) only when a parameter named path exists.
• In getOperationFunction: apply the same pattern for result, streamableMethod, headers, and payload.
• When there is no conflict, the original variable name is preserved — no change to existing generated output.

Testing

• Added a new modular unit test scenario (pathParameterNamedPath.md) that verifies a @path parameter named path generates const path_1 = ... instead of shadowing.
• All 474 unit tests pass.
• Build and lint pass.