Reduce Engine references in expressions

[lahma]

Reduces possibility for hidden engine references and makes expressions more static, allowing later caching too.

Jint.Benchmark.SunSpiderBenchmark

Diff	Method	FileName	Mean	Error	Allocated
Old	Run	3d-cube	219.76 ms	0.612 ms	49017.03 KB
New			216.89 ms (-1%)	0.380 ms	49017.87 KB (0%)
Old	Run	3d-morph	168.84 ms	1.767 ms	48367.71 KB
New			162.61 ms (-4%)	0.237 ms	48368.9 KB (0%)
Old	Run	3d-raytrace	167.10 ms	0.189 ms	88376.8 KB
New			164.49 ms (-2%)	0.369 ms	88376.7 KB (0%)
Old	Run	access-binary-trees	75.98 ms	0.158 ms	60932.51 KB
New			77.33 ms (+2%)	0.207 ms	60933.23 KB (0%)
Old	Run	access-fannkuch	472.85 ms	1.516 ms	136.34 KB
New			458.60 ms (-3%)	3.567 ms	136.34 KB (0%)
Old	Run	access-nbody	190.42 ms	0.484 ms	63665.8 KB
New			194.87 ms (+2%)	0.341 ms	63665.94 KB (0%)
Old	Run	access-nsieve	169.97 ms	0.233 ms	21517.26 KB
New			160.64 ms (-5%)	0.231 ms	21518.16 KB (0%)
Old	Run	bitop(...)-byte [24]	149.14 ms	0.263 ms	56949.13 KB
New			145.16 ms (-3%)	0.357 ms	56951.32 KB (0%)
Old	Run	bitops-bits-in-byte	234.09 ms	1.196 ms	37044.95 KB
New			246.40 ms (+5%)	0.438 ms	37047.82 KB (0%)
Old	Run	bitops-bitwise-and	147.59 ms	0.742 ms	55938.9 KB
New			146.68 ms (-1%)	1.767 ms	55938.9 KB (0%)
Old	Run	bitops-nsieve-bits	220.17 ms	0.160 ms	54072.38 KB
New			215.08 ms (-2%)	0.468 ms	54072.38 KB (0%)
Old	Run	contr(...)rsive [21]	102.95 ms	0.163 ms	83184.26 KB
New			100.32 ms (-3%)	0.168 ms	83184.26 KB (0%)
Old	Run	crypto-aes	144.64 ms	0.159 ms	14010.22 KB
New			141.89 ms (-2%)	0.168 ms	14000.9 KB (0%)
Old	Run	crypto-md5	96.32 ms	0.174 ms	77906.74 KB
New			101.50 ms (+5%)	0.128 ms	77906.77 KB (0%)
Old	Run	crypto-sha1	102.81 ms	0.192 ms	64567.48 KB
New			103.70 ms (+1%)	0.818 ms	64567.56 KB (0%)
Old	Run	date-format-tofte	101.39 ms	0.342 ms	43344.18 KB
New			103.05 ms (+2%)	0.195 ms	43344.33 KB (0%)
Old	Run	date-format-xparb	56.35 ms	0.060 ms	24847.7 KB
New			56.18 ms (0%)	0.064 ms	24847.73 KB (0%)
Old	Run	math-cordic	323.15 ms	1.176 ms	81977.11 KB
New			331.94 ms (+3%)	1.141 ms	81975.49 KB (0%)
Old	Run	math-partial-sums	129.05 ms	0.393 ms	50095.98 KB
New			124.07 ms (-4%)	0.282 ms	50095.95 KB (0%)
Old	Run	math-spectral-norm	132.25 ms	0.267 ms	51833.87 KB
New			120.76 ms (-9%)	0.511 ms	51833.84 KB (0%)
Old	Run	regexp-dna	107.50 ms	0.413 ms	17666.29 KB
New			106.14 ms (-1%)	0.470 ms	17667.31 KB (0%)
Old	Run	string-base64	103.53 ms	0.185 ms	11243.06 KB
New			101.81 ms (-2%)	0.316 ms	11242.54 KB (0%)
Old	Run	string-fasta	192.31 ms	0.418 ms	148053.54 KB
New			198.17 ms (+3%)	0.646 ms	148053.38 KB (0%)
Old	Run	string-tagcloud	70.16 ms	0.836 ms	44033.92 KB
New			70.30 ms (0%)	0.936 ms	44033.83 KB (0%)
Old	Run	string-unpack-code	69.08 ms	0.157 ms	74420.88 KB
New			71.65 ms (+4%)	0.129 ms	74420.91 KB (0%)
Old	Run	strin(...)input [21]	80.86 ms	0.142 ms	39746.38 KB
New			81.21 ms (0%)	0.126 ms	39745.33 KB (0%)