Rename "word" in function/property name to the clearer word

[takahirox]

The emulator uses "word" in function/property name as 32-bit but word should depend on platform. For example, in RISC-V 32-bit word would be 32-bit while in RISC-V 64-bit word would be 64-bit. Then it would be better to replace "word" with the clearer word, like "u32/64".