Add exposed range slider support for facets_exposed_filters (processor + BEF widget)

Problem/Motivation

Facets 3 introduced facets_exposed_filters. For numeric exposed filters, there is currently no dedicated range-slider processor/widget integration that supports:

• min/max range normalization for exposed input
• range boundary calculation from facet results
• Better Exposed Filters slider UI with optional snap-to-available-values
• Solr-specific handling to avoid self-filtered min/max boundaries

Steps to reproduce

1. Create a Search API view with a numeric exposed facet filter.
2. Try to configure it as a range-slider-style exposed filter (BEF).
3. Observe that there is no dedicated exposed-range-slider processor/widget flow in facets_exposed_filters.

Proposed resolution

• Add new processor plugin: exposed_range_slider in facets_exposed_filters.
• Add new BEF widget plugin: facets_exposed_range_slider.
• Add dedicated JS behavior/library for exposed range sliders.
• Extend config schema for processor + BEF widget settings.
• Update hook implementation to:
  • store raw facet results for snap-value extraction
  • force OR operator for Solr when exposed range slider processor is enabled (to prevent self-filtered boundaries)
• Adjust FacetsFilter active-item handling so exposed min/max survives pre-query normalization and rebuilds.

User interface changes

• New processor option: Exposed range slider in facet filter extra options.
• New BEF filter widget: Exposed facet range slider.
• Optional BEF setting: Snap to available facet values.

API changes

• New plugin ID: exposed_range_slider (facets processor).
• New plugin ID: facets_exposed_range_slider (BEF filter widget).
• New schema entries for these plugin configurations.

Release notes snippet

Facets exposed filters now support a dedicated numeric range slider integration (processor + BEF widget), including optional snap-to-values behavior and improved Solr boundary handling.