[clang] ExtractAPI: use zero-based indices for line/column in symbol graph (PR #71753)

[via cfe-commits]

QuietMisdreavus wrote:

An unfortunate side effect of changing the source location representation is that it required changing almost all the ExtractAPI tests. 😅 But the overall diff is rather small.

cc @daniel-grumberg 

https://github.com/llvm/llvm-project/pull/71753