[js/web] update op test schema (#16921)
### Description
update op test schema.
This changes fixes several problems for operator tests for web:
- `opsets` -> `opset`: an operator uses exactly one opset instead of
multiple
- `condition` -> `platformCondition`: make it less confusing
- `inputShapeDefinitions`: allows to test ORT behaviors when it get
no/partial/full shape info.
Added a JSON schema file and also an example file
