symbols: Build in Docker

Created by: chrismwendt

I think this will fix the broken #33689 (which was reverted in https://github.com/sourcegraph/sourcegraph/pull/34316).

Briefly, some tree-sitter grammars need g++, there is no musl-g++, symbols used to be cross-compiled outside of Docker then copied into the image which necessitated a musl compiler. Building in Docker eliminates the need for cross compilation and the ensuing problems.

Full investigation in Slack.

Test plan

TBD