Elaborate on handling of JSON builtin types `integer` and `double`

The spec doesn't describe explicitly enough what happens with JSON builtin types integer and double.

• https://w3c.github.io/json-ld-syntax/#typed-values talks about 64-bit doubles and says "such as" without being exhaustive

3. By using a native JSON type such as number, true, or false.

• https://w3c.github.io/json-ld-syntax/#type-coercion talks about converting strings, not numerics
• #335 describes an unpleasant situation where an integer (eg 3 instead of "3") cannot be used in URL
• this example at the playground produces ex:pi "3.14E0"^^xsd:double (ok) but ex:two "2"^^xsd:integer ?!?!?

{"@context":{"@vocab":"http://example.org/"},
  "pi": 3.14, "two": 2.0000000000000001}

• remove one decimal zero and you get ex:two "2.000000000000001E0"^^xsd:double which means the datatype varies with the lexical precision
• In contrast, Turtle is consistent: 2.0 and 2.0000000000000001 mean xsd:decimal

@msporny @gkellogg
I think the spec should be more explicit what implicit conversions are applied to JSON builtin types, and give some warnings about the examples above.

Read the JSON-LD 1.1 sections on typed values and type coercion, then review issue #335 and reproduce the linked playground examples for integer and double values. Clarify the implicit conversions and lexical-precision behavior, add explicit specification text and warnings, and update the examples so the resulting datatypes are unambiguous.