Backport var declaration and reference resolving performance improvements

[lahma]

Backport #1839

As spec requirements were loosened, makes sense to backport to 3.x. There's performance improvements from now needing to keep track of var global scope names. As Jint takes conformance over performance I believe this is one of the thing that has caused some perf difference compared to more relaxed interpreters.

Jint.Benchmark.DromaeoBenchmark

Diff	Method	Prepared	Toolchain	FileName	Mean	Error	Allocated
Old	Run	False	Default	dromaeo-3d-cube	23.065 ms	0.4453 ms	6315.24 KB
New		False	Default		23.154 ms (0%)	0.1150 ms	6315.24 KB (0%)
Old	Run	False	Default	dromaeo-core-eval	3.974 ms	0.0414 ms	327.5 KB
New		False	Default		4.470 ms (+12%)	0.0272 ms	327.5 KB (0%)
Old	Run	False	Default	dromaeo-object-array	43.011 ms	0.2208 ms	100366.86 KB
New		False	Default		42.965 ms (0%)	0.2314 ms	100366.84 KB (0%)
Old	Run	False	Default	droma(...)egexp [21]	163.435 ms	3.1650 ms	169264.07 KB
New		False	Default		149.457 ms (-9%)	2.2511 ms	151085.44 KB (-11%)
Old	Run	False	Default	droma(...)tring [21]	258.186 ms	5.1544 ms	1321535.77 KB
New		False	Default		254.019 ms (-2%)	5.3817 ms	1315881.84 KB (0%)
Old	Run	False	Default	droma(...)ase64 [21]	52.494 ms	0.2681 ms	6052.13 KB
New		False	Default		47.682 ms (-9%)	0.3240 ms	2372.22 KB (-61%)
Old	Run	True	Default	dromaeo-3d-cube	21.725 ms	0.0881 ms	5966.66 KB
New		True	Default		22.114 ms (+2%)	0.0699 ms	5966.65 KB (0%)
Old	Run	True	Default	dromaeo-core-eval	4.275 ms	0.0236 ms	312.33 KB
New		True	Default		4.201 ms (-2%)	0.0206 ms	312.33 KB (0%)
Old	Run	True	Default	dromaeo-object-array	43.135 ms	0.2668 ms	100320.31 KB
New		True	Default		43.457 ms (+1%)	0.2021 ms	100320.31 KB (0%)
Old	Run	True	Default	droma(...)egexp [21]	124.964 ms	2.3707 ms	166942.69 KB
New		True	Default		113.679 ms (-9%)	1.6015 ms	150766.22 KB (-10%)
Old	Run	True	Default	droma(...)tring [21]	264.836 ms	6.7550 ms	1321333.91 KB
New		True	Default		261.772 ms (-1%)	7.7983 ms	1315878.52 KB (0%)
Old	Run	True	Default	droma(...)ase64 [21]	51.299 ms	0.2805 ms	5948.17 KB
New		True	Default		44.397 ms (-13%)	0.1250 ms	2268.81 KB (-62%)

Jint.Benchmark.EvaluationBenchmark

Diff	Method	Toolchain	Mean	Error	Allocated
Old	Execute	Default	24.302 μs	0.1566 μs	39.39 KB
New		Default	24.641 μs (+1%)	0.3020 μs	39.19 KB (-1%)
Old	Execute_ParsedScript	Default	8.156 μs	0.1338 μs	28.01 KB
New		Default	7.934 μs (-3%)	0.0517 μs	27.8 KB (-1%)

Jint.Benchmark.MinimalScriptBenchmark

Diff	Method	Toolchain	Mean	Error	Allocated
Old	Execute	Default	4.273 μs	0.0489 μs	14.66 KB
New		Default	4.132 μs (-3%)	0.0265 μs	14.46 KB (-1%)
Old	Execute_ParsedScript	Default	2.057 μs	0.0192 μs	12.59 KB
New		Default	1.918 μs (-7%)	0.0084 μs	12.39 KB (-2%)