feat(mat-sort-header): Proposal — Add global token for mat-sort-header icon customization

[Anton-Vladykin]

Feature Description

Summary
Introduce a public DI token to allow apps to replace the default mat-sort-header arrow with app-provided icons/templates in a themable, accessible, and opt-in way.

API (names only)

Token: MAT_SORT_HEADER_ICONS

Config shape: MatSortHeaderIcons with optional keys default, ascending, descending (accepts TemplateRef or sanitized SVG/string)

Use Case

Rationale

Avoids fragile hacks (CSS hiding + DOM mutation) and centralizes app-wide customization.

Keeps behavior backwards-compatible when token is not provided.

Theming

Encourage currentColor so icons follow app theme and runtime CSS variables.

Accessibility

Preserve aria-sort, keep icons decorative (aria-hidden="true"), document when non-decorative icons require additional labeling.

Compatibility

Token is opt-in; default behavior unchanged if not provided.

Reference
Material table styling guidelines: material.angular.dev/components/table/styling.