Fixed a number of data type + signedness issues.
Fixed a number of data type + signedness issues.

The UnbufferedCharStream had a few invalid casts which could lead to wrong numbers. This patch also fixes issue #1619.

parrt/antlr4,parrt/antlr4,ericvergnaud/antlr4,ericvergnaud/antlr4,parrt/antlr4,parrt/antlr4,ericvergnaud/antlr4,parrt/antlr4,ericvergnaud/antlr4,ericvergnaud/antlr4,antlr/antlr4,antlr/antlr4,parrt/antlr4,ericvergnaud/antlr4,antlr/antlr4,parrt/antlr4,ericvergnaud/antlr4,parrt/antlr4,antlr/antlr4,antlr/antlr4,antlr/antlr4,ericvergnaud/antlr4,parrt/antlr4,antlr/antlr4,parrt/antlr4,antlr/antlr4,ericvergnaud/antlr4,ericvergnaud/antlr4,antlr/antlr4,antlr/antlr4