Parentheses for meta fields in format selection syntax

[po5]

Checklist

• I'm reporting a feature request
• I've verified that I'm running youtube-dl version 2020.05.08
• I've searched the bugtracker for similar feature requests including closed ones

Description

Currently, format selection allows doing things like (bestvideo+bestaudio/best)[protocol^=http] which is a handy shortcut for bestvideo+bestaudio[protocol^=http]/best[protocol^=http]

Unfortunately, this is currently only allowed for formats and not meta field filters.

Below is an example of how this would work:
bestvideo[height>=1080][height<1440][fps>30]([vcodec^=av01]/[vcodec=vp9.2]/[vcodec^=vp9])+bestaudio/best
would be equivalent to
(bestvideo[vcodec^=av01][height>=1080][height<1440][fps>30]/bestvideo[vcodec=vp9.2][height>=1080][height<1440][fps>30]/bestvideo[vcodec^=vp9][height>=1080][height<1440][fps>30])+bestaudio/best

[po5]

Related suggestion which would also solve this #5242 (comment)