Remove double lookups on SizeLimitedCache<K, V>, improve performance

[h3xds1nz]

Fixes #4828

Description

While checking out SizeLimitedCache<K, V> yesterday, I've noticed the double lookups on the dictionary and today I've found there's already a corresponding issue for it, hence we should fix it for optimal performance as this is used with glyphs/fonts.

• Use throw helpers over creating new instance of ArgumentNullException directly.
• Remove had even three lookups, so now it just has one.
• Fields that could be readonly have been adjusted.
• Sealed the class, proper naming conventions.
• Node uses auto properties now.

10 capacity, 15 unique additions first, 20 lookups

Method	Mean [ns]	Error [ns]	StdDev [ns]	Gen0	Code Size [B]	Allocated [B]
Original	988.4 ns	9.39 ns	7.84 ns	0.1183	2,045 B	1992 B
PR_EDIT	809.3 ns	9.18 ns	8.14 ns	0.1183	1,820 B	1992 B

Customer Impact

Improved perfomance.

Regression

No.

Testing

Local build, tests with the class.

Risk

Low, just basically compiler warnings.

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