Improve TypeSpec disassembling

[MSDN-WhiteKnight]

• Support custom corelib for built-in types, instead of always using current runtime corelib
• When TypeSpec appears as operand of instruction, it should be disassembled as type in signature

For example: newarr uint8[] instead of newarr [mscorlib]System.Byte[]

https://gitflic.ru/project/smallsoft/ciltools/commit/ad90b7cf3608f387fe7e2bba3f0ed74b2a3157eb
https://gitflic.ru/project/smallsoft/ciltools/commit/67a67a773bd71fd3e1c4cdfa30fc5dd175c5ed17