Split constant and method entries

[vinistock]

Motivation

First step for #1950, which will unblock ancestor linearization

Currently, we are putting all types of entries in the same data structure, mixing constants and methods. This leads to the following issues:

1. Naming conflicts lead to weird scenarios. For example, the Array class and Array() method. We end up having different types of entries for the same name
2. We get worse typing on the index API. For example, in resolve_method, we need to apply a bunch of casts since we know that the returned entry will be a method
3. For Refactor index to nest declarations inside entries #1950 to work properly, we will need to have constants split from methods

Implementation

Created separate data structures for methods. We now have a separate hash and separate prefix tree for methods.

• I benchmarked this and noticed no difference in indexing speed or memory consumption
• While the APIs are now split (e.g.: resolve_constant and resolve_method), I do not think this impacts the DX of using the index. We always know if something is a method call or a constant reference, there would never be a scenario where we are in doubt about which API to invoke

Automated Tests

Adapted our tests.