Update hbar to U+210F from U+0127

[universemaster]

The correct unicode character is ℏ https://www.compart.com/en/unicode/U+210F "Planck Constant Over Two Pi".

However, previously the character was set to ħ https://www.compart.com/en/unicode/U+0127 "Latin Small Letter H with Stroke".

[universemaster]

The entity names given to the characters is confirmed here: https://www.w3.org/2003/entities/2007/htmlmathml-f.ent

<!ENTITY hbar             "&#x0210F;" ><!--PLANCK CONSTANT OVER TWO PI -->
<!ENTITY hslash           "&#x0210F;" ><!--PLANCK CONSTANT OVER TWO PI -->
<!ENTITY hstrok           "&#x00127;" ><!--LATIN SMALL LETTER H WITH STROKE -->

See also https://unicode.org/charts/PDF/U2100.pdf

I also have an open pull request on Julia, JuliaLang/julia#48540