Refined-github: Hide extra spaces in embedded code (`show-whitespace`)

[fregante]

First noted here: https://github.com/sindresorhus/refined-github/pull/2073#issuecomment-495856632

Technically a GitHub bug, but it appears to be pretty consistent: There's an extra space at the beginning and at the end of each line.

show-whitespace should skip these spaces when rendering embedded code.

Screenshot

Live tests

https://github.com/sindresorhus/refined-github/blob/2e4a24d3957c205c7bc49525c69e1fa08593d2ca/readme.md#L107-L112

https://github.com/sindresorhus/refined-github/blob/0b40361983b362d028fac2fe0fed9486134fa41e/package.json#L1-L4

[notlmn]

If implemented, wouldn't the fix be broken for embedded code when GitHub "eventually" fixes it?

Pinging @lukehefson @shayfrendt

[fregante]

Refined GitHub:

[fregante]

If implemented, wouldn't the fix be broken for embedded code when GitHub "eventually" fixes it?

And then we'll fix it again, it's better than waiting until that _maybe_ happens.