WebAssembly.Function and functions of the C-API do not have a function
index. Their index is kAnonymousFuncIndex = -1. Therefore it is
necessary to change the return type of WasmCode::index() from uint to
int.

The changes in WasmFrame::Print produces output like the following:

[9]: CWasmEntryFrame [pc: 0x9d200084091]
[10]: Anonymous wasm wrapper [pc: 0x101c5975c972]
[11]: WASM [wasm://wasm/f4bee83a], function #1 ('fibonacci_wasm'), pc=0x101c5975c5dc (+0x7c), pos=123 (+32)

R=jkummerow@chromium.org

Bug: v8:11713
Change-Id: I1012e92713d64d24ed2a92729dd3c2e4a013b9c0
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2871455Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74355}