[6.x] Use proportional figures by default

[jaygeorge]

Description of the Problem

Closes #15658

The CP sets tabular-nums on body, so every bit of text inherits tabular figures. That includes the content people write in Bard, Markdown, Text and Textarea fields, as well as field instructions. Tabular figures give every digit the same width so columns line up. In running text that makes narrow digits like 1 look loosely and unevenly spaced, so 11 reads almost like "1 1".

What this PR Does

Proportional figures are now the default, and tabular figures only apply where numbers need to line up:

• Listing tables, so dates and numbers stay aligned down a column.
• Number inputs, so the value doesn't shift width as you type or step through it.
• Calendar days, so the grid stays even.
• Date and time picker segments, so the field doesn't jump in width as you change the values.

The Grid, Table, List and Array fieldtypes are left out. They're tables in the markup, but their cells hold content people write.

Why flip the default

Tabular figures are a tool for aligning numbers in columns, not a general-purpose default. That's why fonts like Inter and the system UI fonts ship with proportional figures and leave tabular figures as an opt-in OpenType feature (tnum).

Even in a CP, most numbers sit in running text rather than in columns: labels, instructions, buttons, notifications, and everything people write in their fields. The places where numbers need to line up are few and easy to name: tables, number inputs and date pickers. So it makes sense to opt those in, rather than opting everything else out.

The opt-out route wouldn't hold up anyway. Every new fieldtype, modal or addon that shows prose would need adding to the exclusion list, and they'd keep getting missed.

Pagination totals, revision timestamps and the Updates release notes also switch to proportional figures. They're short runs of text where alignment doesn't matter.

How to Reproduce

1. Add Text, Textarea, Bard and Markdown fields to a blueprint, with instructions like "Maximum 11 items, 111 characters".
2. Create an entry and type the same numbers into each field.
3. The digits now have normal proportional spacing. Dates in entry listings and calendar days still line up.