Allow Value.set_field to throw

[raskad]

While working on some RegExp functions I noticed, that some tests currently fail because Value.set_field always silently no-ops if the property is not writable. For example match sets the lastIndex property multiple times (6.c and 6.f.iii.3.c). It uses the abstract 7.3.4 Set ( O, P, V, Throw ) operation that takes a boolean argument throw and should throw if the property is not writable.

I adjusted the Value.set_field function to make it somewhat similar to 7.3.4 Set ( O, P, V, Throw ). I adjusted all uses of the function to match the spec, if it could be referenced. For uses without clear spec reference, I just set throw to false, so that the current behavior is not impacted.

I'm not sure if changing Value.set_field is the best way forward, but I think an internal function that matches the implementation of 7.3.4 Set ( O, P, V, Throw ) is needed.

[Razican]

Test262 conformance changes:

Test result	master count	PR count	difference
Total	78,897	78,897	0
Passed	26,865	26,871	+6
Ignored	15,628	15,628	0
Failed	36,404	36,398	-6
Panics	0	0	0
Conformance	34.05%	34.06%	+0.01%

Fixed tests:

test/built-ins/RegExp/prototype/exec/y-fail-lastindex-no-write.js [strict mode] (previously Failed)
test/built-ins/RegExp/prototype/exec/y-fail-lastindex-no-write.js (previously Failed)
test/built-ins/RegExp/prototype/Symbol.search/set-lastindex-init-err.js [strict mode] (previously Failed)
test/built-ins/RegExp/prototype/Symbol.search/set-lastindex-init-err.js (previously Failed)
test/built-ins/RegExp/prototype/test/y-fail-lastindex-no-write.js [strict mode] (previously Failed)
test/built-ins/RegExp/prototype/test/y-fail-lastindex-no-write.js (previously Failed)

[RageKnify]

Seems right to me, I think most of this will change with separation of Value and Object, but it's still nice to have this to fix the tests while that isn't done.