This CL modifies the following to be LEB128:
* Function table indices
* Import table signature indices
* Export table function indices
* Function signature param count
* br/br_if break depth
* br_table target count
* block/loop expression count

Still to do:
* Import/export names (LEB128 count + inline data)
* Data segments (LEB128 offset + size + inline data)
* Function header stuff (should seperate into function sig and body sections)
* Memory access alignment + offset (still discussing)

BUG=
R=titzer@chromium.org

Review URL: https://codereview.chromium.org/1775873002

Cr-Commit-Position: refs/heads/master@{#34603}