[18.0][IMP] hr_shift: use employee name instead of weekday in line display_…

[cvinh]

…name

hr.shift.planning.line._compute_display_name currently produces '{weekday} - {template or state}'. That format is redundant in every place the display_name is actually shown to end users:

• On the calendar view, the weekday is the column position, so writing it inside the block label just repeats what the grid already conveys.
• On the list and form views, day_number is a dedicated field already rendered as its own column or field, so the weekday appears twice on the same row.

Meanwhile the field the display_name lacks is the employee, which makes the identity of a line indistinguishable from another line of the same planning on the same weekday (two employees sharing 'Wednesday - Morning' get the exact same display_name, so any breadcrumb, popover title, chatter mention or mail template that relies on display_name cannot tell them apart).

Replace the weekday by the employee's name in the format expression and update @api.depends accordingly. day_number remains fully available through its own field wherever it is needed (calendar column, list column, form field). The employee full name is used as-is, without truncation, consistent with how it appears in every other HR view.