feat(material/sort): header icon customization

[lekhmanrus]

• Add optional icons (SortHeaderIcons) configuration object to MAT_SORT_DEFAULT_OPTIONS for customizing the icons used by mat-sort-header
• Add matSortIconsTemplate template for the sort icons to [mat-sort-header]. { isDisabled: boolean; direction: 'asc' | 'desc' | ''; isSorted: boolean } passed as context.

Close #32002, #30563

[crisbeto]

I was actually thinking to just let users project in their own icon: #32016

[lekhmanrus]

Thanks @crisbeto. That makes sense, allowing users to project their own icon seems like a cleaner approach.

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