Implement Context

[jameslahm]

Now the realm api is very simple

let rt = Runtime::new(...)
let ctx1 = Context::new(rt)
let ctx2 = Context::new(rt)
// ctx1 and ctx2 are standalone realm, not influence each other
ctx1.eval()
ctx2.eval()

TODO

• [x] serialize and deserialize
• [x] allocate context on heap

[playXE]

Wow! That's quite a lot of work! But I do not like that Context resides on the stack, I guess it should be always allocated on the GC heap instead so we can copy it and also store it in JsGlobal in safe way without using *mut Context.

[jameslahm]

There are still some problems with tests. I'll look into it.

[github-actions[bot]]

Test262 conformance changes:

Test result	Dev count	PR count	Difference
Total	79,437	79,437	0
Passed	13,739	13,738	-1
Ignored	24,388	24,388	0
Failed	39,972	39,468	-504
Panics	1,338	1,843	+505
Conformance	17.30	17.29	-0.00%

Base Failed But New Passed

``` 1. [non-strict] test262/test/built-ins/String/prototype/padStart/exception-fill-string-symbol.js 2. [strict] test262/test/built-ins/Object/keys/15.2.3.14-4-1.js 3. [strict] test262/test/built-ins/String/prototype/padStart/exception-fill-string-symbol.js 4. [strict] test262/test/built-ins/Symbol/prototype/valueOf/this-val-symbol.js 5. [strict] test262/test/built-ins/Symbol/prototype/constructor.js 6. [strict] test262/test/built-ins/String/prototype/padStart/exception-symbol.js 7. [non-strict] test262/test/built-ins/Promise/prototype/S25.4.5_A3.1_T1.js 8. [non-strict] test262/test/built-ins/Symbol/prototype/constructor.js 9. [non-strict] test262/test/built-ins/String/prototype/padStart/exception-symbol.js 10. [non-strict] test262/test/built-ins/Symbol/prototype/valueOf/this-val-symbol.js 11. [strict] test262/test/built-ins/Promise/prototype/S25.4.5_A3.1_T1.js ```

New Failed But Base Passed

``` 1. [strict] test262/test/built-ins/String/prototype/padStart/fill-string-omitted.js 2. [non-strict] test262/test/built-ins/String/prototype/padStart/fill-string-omitted.js 3. [strict] test262/test/built-ins/String/prototype/padStart/observable-operations.js 4. [non-strict] test262/test/built-ins/String/prototype/padStart/observable-operations.js 5. [strict] test262/test/built-ins/String/prototype/padStart/max-length-not-greater-than-string.js 6. [strict] test262/test/built-ins/String/prototype/trimStart/this-value-boolean.js 7. [non-strict] test262/test/built-ins/String/prototype/trimStart/this-value-boolean.js 8. [strict] test262/test/built-ins/String/prototype/padStart/fill-string-empty.js 9. [non-strict] test262/test/built-ins/String/prototype/trimStart/this-value-line-terminator.js 10. [non-strict] test262/test/built-ins/String/prototype/padStart/max-length-not-greater-than-string.js 11. [non-strict] test262/test/built-ins/String/prototype/padStart/fill-string-empty.js 12. [strict] test262/test/built-ins/String/prototype/trimStart/this-value-line-terminator.js ```