[all components][RFC] Refine logging strategy

Context

This is a follow-up on #15343. Looking at the components (under /packages/*), we can count the following usage frequency of the different logging methods:

• console.error() x69
• console.warn() x25

Historically, React used to use console.warn(). It was changed in https://github.com/facebook/react/pull/3440 to benefit from the stack trace of console.error(). But fast forward to 2020, Chrome dev tools now support stack trace for console.warn() too. Proof:

Problem

It doesn't seem that there is any rule or convention around when to use error over warn. Do we have an improvement opportunity here? Could we use it as leverage to help developers that need to prioritize which problem they should focus on first?

Proposal

What do you think of:

• If we are unsure, better say it's an error over warn to be safe.
• console.error we use it for cases that are important. It can be a crash of the page, explaining what went wrong, or creating awareness about a significantly wrong user-experience. For instance:
  https://github.com/mui/material-ui/blob/56a1141631905f65c1f5c1d5f41702016327a4ad/packages/material-ui/src/FormControl/FormControl.js#L135-L140
• console.warn is used as soon as something is not right, leading to incorrect behavior but not critical. For instance, these should be warnings:
  https://github.com/mui/material-ui/blob/56a1141631905f65c1f5c1d5f41702016327a4ad/packages/material-ui/src/StepContent/StepContent.js#L44-L46
  https://github.com/mui/material-ui/blob/56a1141631905f65c1f5c1d5f41702016327a4ad/packages/material-ui-icons/src/Motorcycle.js#L4-L8
  https://github.com/mui/material-ui/blob/56a1141631905f65c1f5c1d5f41702016327a4ad/packages/material-ui/src/Breadcrumbs/Breadcrumbs.js#L81-L86
  https://github.com/mui/material-ui/blob/56a1141631905f65c1f5c1d5f41702016327a4ad/packages/material-ui/src/GridList/GridList.js#L46-L50

Start by auditing the console.error() and console.warn() usages under /packages/* against the proposed severity guidelines and referenced examples. Done would be an agreed logging convention and a concrete, reviewed plan for applying it across components; the issue names no target file or test.