Port 0c4b8ff4

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

R=gdeepti@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com
BUG=
LOG=N

Review-Url: https://codereview.chromium.org/2625683004
Cr-Commit-Position: refs/heads/master@{#42201}