port 0c4b8ff4 (r42192)

  original commit message:
   - Refactor Dispatch tables to have separate function, signature tables
   - New Relocation type for WasmFunctionTableReference, assembler, compiler support.
   - RelocInfo helper functions for Wasm references

BUG=

Review-Url: https://codereview.chromium.org/2623133002
Cr-Commit-Position: refs/heads/master@{#42208}