Cleanup custom dictionary implementations

[lahma]

Simplifying and adding idiomatic GetValueRefOrNullRef and GetValueRefOrAddDefault. This paves ground for further things.

[lahma]

No obvious regressions, maybe minor improvements due to better ref handling for structs.

Jint.Benchmark.DromaeoBenchmark

Diff	Method	FileName	Mean	Error	Allocated
Old	Run	dromaeo-3d-cube	16.193 ms	0.1910 ms	6303.54 KB
New			15.464 ms (-5%)	0.2101 ms	6303.53 KB (0%)
Old	Run	dromaeo-core-eval	3.193 ms	0.0396 ms	327.5 KB
New			3.053 ms (-4%)	0.0326 ms	327.5 KB (0%)
Old	Run	dromaeo-object-array	32.472 ms	0.4626 ms	96259.28 KB
New			32.765 ms (+1%)	0.2252 ms	96259.28 KB (0%)
Old	Run	droma(...)egexp [21]	125.202 ms	2.4769 ms	152142.39 KB
New			127.352 ms (+2%)	2.5013 ms	150088.89 KB (-1%)
Old	Run	droma(...)tring [21]	239.647 ms	6.7246 ms	1315932.8 KB
New			238.093 ms (-1%)	5.0486 ms	1315960.57 KB (0%)
Old	Run	droma(...)ase64 [21]	35.450 ms	0.4659 ms	2367.54 KB
New			35.467 ms (0%)	0.6157 ms	2367.54 KB (0%)
Old	Run	dromaeo-3d-cube	15.285 ms	0.1544 ms	5965.27 KB
New			15.007 ms (-2%)	0.0945 ms	5965.28 KB (0%)
Old	Run	dromaeo-core-eval	3.066 ms	0.0293 ms	312.43 KB
New			3.081 ms (0%)	0.0336 ms	312.43 KB (0%)
Old	Run	dromaeo-object-array	32.312 ms	0.3624 ms	96211.88 KB
New			32.930 ms (+2%)	0.4832 ms	96211.88 KB (0%)
Old	Run	droma(...)egexp [21]	93.031 ms	1.8569 ms	151918.6 KB
New			94.901 ms (+2%)	1.8855 ms	149797.5 KB (-1%)
Old	Run	droma(...)tring [21]	252.667 ms	9.4087 ms	1315776.21 KB
New			243.684 ms (-4%)	8.7360 ms	1315651.8 KB (0%)
Old	Run	droma(...)ase64 [21]	35.431 ms	0.5152 ms	2268.38 KB
New			35.802 ms (+1%)	0.4183 ms	2268.36 KB (0%)

Jint.Benchmark.SunSpiderBenchmark

Diff	Method	FileName	Mean	Error	Allocated
Old	Run	3d-cube	123.76 ms	1.827 ms	45164.84 KB
New			120.55 ms (-3%)	1.560 ms	45164.84 KB (0%)
Old	Run	3d-morph	106.48 ms	1.337 ms	46258.14 KB
New			111.77 ms (+5%)	0.950 ms	46258.14 KB (0%)
Old	Run	3d-raytrace	117.68 ms	1.217 ms	86418.77 KB
New			116.88 ms (-1%)	2.309 ms	86418.77 KB (0%)
Old	Run	access-binary-trees	64.11 ms	1.254 ms	62249.22 KB
New			65.64 ms (+2%)	0.804 ms	62249.23 KB (0%)
Old	Run	access-fannkuch	285.92 ms	1.789 ms	103.84 KB
New			273.34 ms (-4%)	3.899 ms	103.84 KB (0%)
Old	Run	access-nbody	128.22 ms	1.497 ms	53295.23 KB
New			127.70 ms (0%)	1.141 ms	53295.32 KB (0%)
Old	Run	access-nsieve	94.19 ms	1.349 ms	17142.67 KB
New			93.40 ms (-1%)	0.846 ms	17142.67 KB (0%)
Old	Run	bitop(...)-byte [24]	100.98 ms	0.456 ms	61948.39 KB
New			99.49 ms (-1%)	1.142 ms	61948.44 KB (0%)
Old	Run	bitops-bits-in-byte	146.21 ms	1.037 ms	40544.67 KB
New			149.18 ms (+2%)	1.235 ms	40544.67 KB (0%)
Old	Run	bitops-bitwise-and	84.43 ms	0.515 ms	55938.96 KB
New			85.03 ms (+1%)	0.967 ms	55939.01 KB (0%)
Old	Run	bitops-nsieve-bits	139.24 ms	2.048 ms	53916.36 KB
New			137.31 ms (-1%)	1.341 ms	53916.36 KB (0%)
Old	Run	contr(...)rsive [21]	78.36 ms	1.238 ms	92772.97 KB
New			78.10 ms (0%)	1.530 ms	92772.97 KB (0%)
Old	Run	crypto-aes	85.42 ms	1.232 ms	10750.3 KB
New			82.77 ms (-3%)	0.746 ms	10748.13 KB (0%)
Old	Run	crypto-md5	73.42 ms	1.074 ms	82176.44 KB
New			69.22 ms (-6%)	0.960 ms	82176.43 KB (0%)
Old	Run	crypto-sha1	69.44 ms	0.890 ms	68861.22 KB
New			67.08 ms (-3%)	0.732 ms	68861.22 KB (0%)
Old	Run	date-format-tofte	67.65 ms	0.821 ms	54569.06 KB
New			65.02 ms (-4%)	0.683 ms	54569.06 KB (0%)
Old	Run	date-format-xparb	37.85 ms	0.742 ms	26400.13 KB
New			38.89 ms (+3%)	0.627 ms	26400.13 KB (0%)
Old	Run	math-cordic	214.60 ms	2.112 ms	86859.77 KB
New			217.93 ms (+2%)	2.920 ms	86859.77 KB (0%)
Old	Run	math-partial-sums	76.10 ms	0.484 ms	49367.9 KB
New			75.45 ms (-1%)	0.822 ms	49367.9 KB (0%)
Old	Run	math-spectral-norm	82.50 ms	1.559 ms	56617.52 KB
New			81.70 ms (-1%)	1.615 ms	56617.52 KB (0%)
Old	Run	regexp-dna	100.24 ms	1.070 ms	16828.1 KB
New			100.94 ms (+1%)	1.371 ms	16825.89 KB (0%)
Old	Run	string-base64	52.22 ms	0.492 ms	3156.24 KB
New			52.98 ms (+1%)	0.630 ms	3156.24 KB (0%)
Old	Run	string-fasta	112.80 ms	1.016 ms	104785.78 KB
New			114.32 ms (+1%)	2.155 ms	104786.09 KB (0%)
Old	Run	string-tagcloud	53.93 ms	1.074 ms	42042.91 KB
New			53.18 ms (-1%)	1.054 ms	42042.57 KB (0%)
Old	Run	string-unpack-code	52.23 ms	0.904 ms	73810.7 KB
New			52.58 ms (+1%)	1.012 ms	73810.71 KB (0%)
Old	Run	strin(...)input [21]	43.06 ms	0.485 ms	20687.73 KB
New			43.83 ms (+2%)	0.417 ms	20687.73 KB (0%)

[sebastienros]

Simplifying -> AddDangerous ... But I trust you

[lahma]

Simplifying -> AddDangerous ... But I trust you

Hah, it just for occasions when you know that thing is going to be added and no need to update/check existing value.