feat: support non-ascii characters in for/each title placeholders - #10773

Description

although it's unusual, it's theoretically possible to use non-ascii characters in variable names. For example:

// math-heavy code might use greek letters:
it.each`
  ω    | Σ
  ${1} | ${5}
  ${2} | ${10}
`('returns true when $ω is < $Σ', ({ ω, Σ }) => {
  // ...
});


// and I suppose this works in some other languages too:
it.each`
  时间戳 | 结果
  ${1}  | ${5}
  ${2}  | ${10}
`('returns $结果 given $时间戳', ({ 结果, 时间戳 }) => {
  // ...
});

currently, the test title formatter use RegEx \w, so it doesn't support non-ascii values. \p{ID_Continue} has been supported since node v10, see Unicode's UAX31-D1 for more info.

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