Devanagari: 4.5 Counters, Lists - add usage examples, add reference documentation, specs being referred to

[alolita]

https://w3c.github.io/iip/gap-analysis/deva-gap.html#counters

This issue needs to have more documentation on what advanced level support means in this context.

Which spec is being referred to? Link please.

Provide usage examples, related tests.

For Deva: devanagari
devanagari numbering (e.g., १, २, ३, ..., ९८, ९९, १००).
@counter-style devanagari {
system: numeric;
symbols: "\966" "\967" "\968" "\969" "\96A" "\96B" "\96C" "\96D" "\96E" "\96F";
/* ० १ २ ३ ४ ५ ६ ७ ८ ९ */

@counter-style hindi {
system: alphabetic;
symbols: '\915' '\916' '\917' '\918' '\919' '\91A' '\91B' '\91C' '\91D' '\91E' '\91F' '\920' '\921' '\922' '\923' '\924' '\925' '\926' '\927' '\928' '\92A' '\92B' '\92C' '\92D' '\92E' '\92F' '\930' '\932' '\935' '\936' '\937' '\938' '\939';
/* symbols: 'क' 'ख' 'ग' 'घ' 'ङ' 'च' 'छ' 'ज' 'झ' 'ञ' 'ट' 'ठ' 'ड' 'ढ' 'ण' 'त' 'थ' 'द' 'ध' 'न' 'प' 'फ' 'ब' 'भ' 'म' 'य' 'र' 'ल' 'व' 'श' 'ष' 'स' 'ह'; */

[r12a]

Which spec is being referred to? Link please.

These are already linked to in the GA doc.
Spec: https://www.w3.org/TR/css-counter-styles-3/#simple-numeric
Doc: https://w3c.github.io/predefined-counter-styles/#devanagari-styles

Provide usage examples, related tests.

Tests with results are available at
https://www.w3.org/International/tests/#css3-counter-styles
https://www.w3.org/International/tests/#predefined-counter-styles

[r12a]

The PR at #48 adds information about tests and results for Devanagari, Bengali, and Tamil. We need to consider the impact of those test results and add a summary of that to each document.