Long numbers are sometimes hard to read in the numeric tooltip. To
improve readability, this PR adds language-specific digit separators to
the numeric tooltip.
Decimal numbers are grouped into chunks of three digits while
hexadecimal numbers are grouped into chunks of length four.
The digit separator is language-specific and chosen so that the number
is a valid token in the source language.
[Examples](https://godbolt.org/z/s86cMbjeK):
* for C++, hovering the number `8583909746840200552` shows this tooltip:
`8'583'909'746'840'200'552 = 0x7720'2C6F'6C6C'6568 =
6.5188685003648344e+265`
* for Python, hovering the number `-12345678` shows this tooltip:
`-123_456_789 = 0xFFFF_FFFF_F8A4_32EB = -2.66427945e+34f`
For languages that don’t have a `digitSeparator` set, the tooltip is not
changed.
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