Update generics overview

[josh11b]

This reflects changes from a number of approved proposals:

• Checked and template generic terminology #2138 : "generic" -> "checked generic", "template" -> "template generic"
• Types are values of type type #2360 : "type", "facet type", "facet". Note: I am not using the term "generic type" from Types are values of type type #2360 since that meaning conflicts with the generally accepted meaning of "generic type" of a type with a compile-time parameter.
• Consistent class and interface syntax #2760 / Terminology for internal and external implementations #2770 : internal/external impl -> extending impl
• Expression phase terminology #2964 : "symbolic constant" and "template constant"

[zygoloid]

Suggested change

	A function can have a mix of checked, template, and regular parameters. A
	checked parameter is defined using a symbolic binding pattern, a template
	parameter using a template binding pattern, and a regular parameter using a
	runtime binding pattern. Likewise, it's allowed to pass a symbolic or template
	A function can have a mix of checked, template, and regular parameters. A
	checked parameter is defined using a symbolic binding pattern, a template
	parameter is defined using a template binding pattern, and a regular parameter is defined using a
	runtime binding pattern. Likewise, it's allowed to pass a symbolic or template

I originally read this as

A checked parameter is defined using (a symbolic binding pattern, a template parameter using a template binding pattern, and a regular parameter using a runtime binding pattern).

Alternatively, I think something like this could work:

Each kind of parameter is defined using a different syntax: a checked parameter is uses a symbolic binding pattern, a template parameter uses a template binding pattern, and a regular parameter uses a runtime binding pattern.

[josh11b]

I used the alternative, but also noticed I needed to update the next sentence.