Merge 'Move value functions to separate file' from Pedro Muniz

Makes it easier to visualize what is related to Value and what is
related to opcodes. This will also facilitate in my next PR to
generalize certain function over `Value` and `ValueRef` as listed in
#2304

Closes #3919

core/vdbe/mod.rs

@@ -24,6 +24,7 @@ pub mod insn;
 pub mod likeop;
 pub mod metrics;
 pub mod sorter;
+pub mod value;
 
 use crate::{
     error::LimboError,