[LLDB] Add more helper functions to ValueObject class. (#87197)

Create additional helper functions for the ValueObject class, for:
  - returning the value as an APSInt or APFloat
  - additional type casting options
  - additional ways to create ValueObjects from various types of data
  - dereferencing a ValueObject

These helper functions are needed for implementing the Data Inspection
Language, described in
https://discourse.llvm.org/t/rfc-data-inspection-language/69893