reflect: add TypeAssert

[jakebailey]

This function was missing, leading to:

# github.com/go-json-experiment/json
../../go/pkg/mod/github.com/go-json-experiment/json@v0.0.0-20251027170946-4849db3c2f7e/arshal_funcs.go:181:20: undefined: reflect.TypeAssert
../../go/pkg/mod/github.com/go-json-experiment/json@v0.0.0-20251027170946-4849db3c2f7e/arshal_funcs.go:227:20: undefined: reflect.TypeAssert
../../go/pkg/mod/github.com/go-json-experiment/json@v0.0.0-20251027170946-4849db3c2f7e/arshal_funcs.go:275:20: undefined: reflect.TypeAssert
../../go/pkg/mod/github.com/go-json-experiment/json@v0.0.0-20251027170946-4849db3c2f7e/arshal_funcs.go:314:20: undefined: reflect.TypeAssert
../../go/pkg/mod/github.com/go-json-experiment/json@v0.0.0-20251027170946-4849db3c2f7e/arshal_inlined.go:54:19: undefined: reflect.TypeAssert
../../go/pkg/mod/github.com/go-json-experiment/json@v0.0.0-20251027170946-4849db3c2f7e/arshal_inlined.go:177:19: undefined: reflect.TypeAssert
../../go/pkg/mod/github.com/go-json-experiment/json@v0.0.0-20251027170946-4849db3c2f7e/arshal_methods.go:133:28: undefined: reflect.TypeAssert
../../go/pkg/mod/github.com/go-json-experiment/json@v0.0.0-20251027170946-4849db3c2f7e/arshal_methods.go:159:27: undefined: reflect.TypeAssert
../../go/pkg/mod/github.com/go-json-experiment/json@v0.0.0-20251027170946-4849db3c2f7e/arshal_methods.go:182:28: undefined: reflect.TypeAssert
../../go/pkg/mod/github.com/go-json-experiment/json@v0.0.0-20251027170946-4849db3c2f7e/arshal_methods.go:216:28: undefined: reflect.TypeAssert
../../go/pkg/mod/github.com/go-json-experiment/json@v0.0.0-20251027170946-4849db3c2f7e/arshal_methods.go:256:30: undefined: reflect.TypeAssert
../../go/pkg/mod/github.com/go-json-experiment/json@v0.0.0-20251027170946-4849db3c2f7e/arshal_methods.go:283:30: undefined: reflect.TypeAssert
../../go/pkg/mod/github.com/go-json-experiment/json@v0.0.0-20251027170946-4849db3c2f7e/arshal_methods.go:310:30: undefined: reflect.TypeAssert
../../go/pkg/mod/github.com/go-json-experiment/json@v0.0.0-20251027170946-4849db3c2f7e/arshal_time.go:60:22: undefined: reflect.TypeAssert
../../go/pkg/mod/github.com/go-json-experiment/json@v0.0.0-20251027170946-4849db3c2f7e/arshal_time.go:87:21: undefined: reflect.TypeAssert
../../go/pkg/mod/github.com/go-json-experiment/json@v0.0.0-20251027170946-4849db3c2f7e/arshal_time.go:131:22: undefined: reflect.TypeAssert
../../go/pkg/mod/github.com/go-json-experiment/json@v0.0.0-20251027170946-4849db3c2f7e/arshal_time.go:157:21: undefined: reflect.TypeAssert

I ported the (theoreticlaly faster) reflectlite version of this, rather than just doing v.Interface().(T), and copied the tests. I am not sure what's typical for this.

[jakebailey]

Hm, make test doesn't complain about this; I'll have to figure out how to run these tests myself.

I can always flip it to the less optimal version if I don't figure out the deal here; perhaps the pointer arithmetic done in big Go does not apply to tinygo

[dgryski]

LGTM. Just needs to skip the panic test on wasi.

[dgryski]

LGTM

[jakebailey]

--- FAIL: TestTypeAssertPanic (0.00s)
    recover not supported
    SkipNow is incomplete, requires runtime.Goexit()

I guess I should just log and return instead.

[dgryski]

LGTM

[deadprogram]

Thanks for the addition @jakebailey and to @dgryski for doing the reviewing. Now merging.