Better handle auto type conversions

[liach]

Sometimes, some constants would be stored as a narrower type and be used as a wider type downstream:
For example:
In the game state change s2c packet, a few values for demo states are stored as integers but always read as floats.
In the packet byte buf, the max nbt size is an int but passed to a ctor that takes longs; the default max string length is a short but the length accepts an int.

Currently, a workaround is to specify a descriptor and a value. However, the problem with that is unpick seems to generate wrong getstatic opcodes with wrong descriptors (than use instruction like i2f), because what i see in decompiler is unresolved field references.