read unsigned bytecode operands in CodeHTML disassembler

[rootvector2]

CodeHTML.codeToHTML disassembles byte code independently of the class-file model and read wide local-variable indices, field/method/class/LDC_W constant-pool indices and the multianewarray dimension count with signed readShort()/readByte(), so a class whose operand is >= 0x8000 (or dimensions >= 128) sign-extends to a negative value and the generated _code.html shows a negative slot/dimension or does a wrong constant-pool lookup; the reference disassembler Utility.codeToString already reads all of these as unsigned, so this makes codeToHTML match it. Found by diffing the two disassemblers operand by operand.

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