[Debuginfo] improve enum value formatting in LLDB for better readability

[nilptr]

TL;DR: When debugging with CodeLLDB, I noticed enum values were often hard to read because LLDB lists every possible variant, resulting in a verbose and cluttered view, even though only one variant is actually valid. Interestingly, raw enum types display nicely. After some investigation, I found that &enum values get classified as Other, so it falls back to DefaultSyntheticProvider, which causes this verbose output.

What does this PR do?

This PR contains 2 commits:

1. change the enum value formatting from showing 2 separate fields (value for attached data and $discr$ for the discriminator) to a concise <readable variant name>: <attached data> format
2. dereference pointer types in classify_rust_type so that it can return more accurate type for reference type

Self-test proof

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This PR was rebased onto a different master commit! Check out the changes with our range-diff.