fix: prefer relocated source path suffixes

[immanuwell]

Absolute DWARF paths can fall back to the first matching basename in web.
With both a/basic.c and src/basic.c, a /src/basic.c link shows a/basic.c

The resolver now tries relocated path suffixes first, then keeps the basename fallback

Repro:

1. Put different files at a/basic.c and src/basic.c
2. Run stackwhere web collection.o --source-dir .
3. Open /source?file=%2Fsrc%2Fbasic.c

Before it picks a/basic.c, now it picks src/basic.c

Tests: go test ./..., go test -race ./..., go vet ./..., golangci-lint run