DB<26> x q(It's\ )
0  'It\'s\\ '
  DB<27> x quotemeta q(It's\ )
0  'It\\\'s\\\\\\ '

...

  DB<29> x quotemeta q(It's\x)
0  'It\\\'s\\\\x'
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FWIW you can write a regex which consumes every paired backslash in an or'ed condition before replacing single quotes/backslashes.

But a real test-cases are imperative here.

update

this shows that the input format should be well defined too

  DB<37> dd quotemeta q(It's\x\\)
"It\\'s\\\\x\\\\"
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