Change all built in named entities to numeric entities

[Chase-san]

In the core code, this should be done for easier compatibility with html 5. Polyglot markup only has 5 named entities. These need not be changed. They are amp, lt, gt, apos, and quot.

Named entities are case-sensitive, which may cause problems. Numbers do not have case, which means they do not have this issue.

Changing entities from named to numeric is a rather small task and it should greatly help overall portability. I am unaware of any implementation that supports only named entities.

Also numeric entities should be infinitesimally quicker to look up by browsers, being a numeric index.

Example

• change › to ›
• change ← to ←

and so on

[ocean90]

#13341, #9030