fix(locale): use correct English ordinal in en-ca, en-ie, en-il, en-sg

[greymoth-jp]

What

en-ca, en-ie, en-il and en-sg still carry the placeholder ordinal: n => n, so format('Do') returns the bare day number for them:

dayjs('2021-01-21').locale('en-au').format('Do') // "21st"
dayjs('2021-01-21').locale('en-ca').format('Do') // "21"  (expected "21st")

(Do comes from the advancedFormat plugin.)

The other English locales already define the standard English ordinal function: en, en-au, en-gb, en-in, en-nz, en-tt. English ordinals (1st/2nd/3rd, 11th/21st) are the same across these regions, so the four locales above were simply missing the function rather than intentionally different. This is the same change #2878 made for en-au ("Use the same ordinal as moment"); moment also defines the full ordinal for en-ca, en-ie, en-il and en-sg.

Fix

Reuse the existing English ordinal function in the four locales.

Test

Added an ordinal parity check in test/locale/en.test.js that compares format('Do') against moment for days 1 to 31 in each of the four locales. It fails on the old n => n and passes with the change. The full jest suite is green and eslint passes.