fix(toolbar): eliminate duplicate id in toolbar_input_select()

[gadenbuie]

Fixes #1350

Summary

toolbar_input_select() was generating HTML with duplicate id attributes on both the container div and the inner select element. This violates HTML standards and can cause issues with JavaScript selectors and accessibility tools.

The fix assigns a distinct ID to the select element using the pattern {id}--select (double dash to avoid conflicts with Shiny module inputs), while the container retains its ID for Shiny's input binding system. The label's for attribute is updated to point to the new select ID.

Verification

Before the fix, toolbar_input_select("select", label = "Choose", choices = c("A", "B")) produced:

<div id="select" class="bslib-toolbar-input-select shiny-input-container">
  <label id="select-label" for="select">...</label>
  <select id="select">...</select>  <!-- duplicate id! -->
</div>

After the fix, it produces:

<div id="select" class="bslib-toolbar-input-select shiny-input-container">
  <label id="select--label" for="select--select">...</label>
  <select id="select--select">...</select>  <!-- unique id -->
</div>