VTT sources and fonts built with build chain are incompatible

The glyphs in the VTT hinted sources have nodes which don't match the glyphs generated from the build chain. This means we won't be able to successfully transfer the hints from the VTT sources to the build chain fonts.

_glyph: a | top path: build chain | bottom path: VTT source_

If I run `gftools check-vtt-compatibility --compatible ./source/TTF_VTT_source/OpenSans-Roman.ttf ./fonts/variable_ttf/OpenSans-Roman-VF.ttf`, I get the following incompatible glyphs:

> partialdiff, ycircumflex, dollar.rvrn, alpha, ucircumflex, g893, uni047C, ae, ecircumflex, comma, D, divide, estimated, braceleft, g887, jcircumflex, ring, exclamdown, quotedblbase, adieresis, tildecomb, X, upsilondieresis, wcircumflex, semicolon, quotereversed, seven.numr, U, phi, V, tau, Abreve, ccaron, germandbls, obreve, perthousand, d, circumflex, OE, emacron, ldot, greater, quotedbl, copyright, R, rcaron, sigma, longs, S, j, g888, brokenbar, periodcentered, A, product, equal, c, umacron, theta, less, r, zeta, G, ccedilla, uni047C.rvrn, xi, second, Idieresis.ss01, hungarumlaut, Lambda, slash, amacron, ubreve, Aringacute, numbersign, Oslash, notequal, K, ampersand, kgreenlandic, nine, gravecomb, backslash, caron.alt, iogonek, aogonek, uring, one.lf, lambda, p, uni047F, g, ecaron, zero.osf, itilde, Idotaccent.ss01, hyphen, thorn, aring, endash, ordfeminine, dieresis, three.numr, ocircumflex, y, braceright, idieresis, g891, one.numr, two.numr, zdotaccent, psi, omicron, gcircumflex.ss02, underscore, gbreve, e, Omegatonos, macron, tonos, sterling, three.osf, dieresistonos, Uhorn, Thorn, ohorn, g.ss02, six.osf, scedilla, Pi, g890, Phi, guilsinglleft, ogonek, napostrophe, infinity, quotedblright, hbar, Q, bracketleft, x, period, bar, bullet, t, gcircumflex, cyrillicbighookUC, Amacron, five.osf, Lslash, eight, dollar, W, two, iacute, ydieresis, dotaccent, question, AE, radical, h, H, s, N, gamma, fraction, logicalnot, franc, anoteleia, quoteright, zero.numr, Imacron, four.numr, z, eight.numr, parenleft, daggerdbl, rho, ebreve, minus, Y, gdotaccent.ss02, peseta, Ibreve.ss01, nine.numr, quotesingle, E, g889, acutecomb, at, asterisk, oe, Z, aringacute, one.osf, asciicircum, asciitilde, emdash, quotedblleft, dcroat, I.ss01, delta, wdieresis, scircumflex, pi, cyrillicbighookLC, paragraph, trademark, l, florin, zcaron, L, multiply, Iotadieresis.ss01, seven, o, Psi, quotesinglbase, Hcircumflex, c.rvrn, ccircumflex, edotaccent, four.osf, two.osf, udieresis, tbar, nu, uni047B, Ldot, ordmasculine, uhungarumlaut, upsilon, abreve, uogonek, gbreve.ss02, Acircumflex, chi, underscoredbl, Adieresis, k, Eth, m, bracketright, P, Aogonek, omega, Emacron, one, Aringacute.rvrn, igrave, Icircumflex.ss01, ellipsis, dotbelowcomb, lessequal, gdotaccent, lozenge, dagger, oslash, B, odieresis, uni047A, ncaron, zero, hcircumflex, Sigma, Ohorn, n, g894, scaron, ohungarumlaut, cedilla, summation, epsilon, uni047D, a, O, three, Imacron.ss01, percent, Eogonek, icircumflex, colon, edieresis, M, registered, integral, Gamma, cent, u, uhorn, guilsinglright, kappa, breve, four, b, cdotaccent, v, currency, J, omacron, degree, beta, Upsilon, q, g892, T, f, hookabovecomb, cyrillichookleft, iota, dong, greaterequal, Tbar, quoteleft, section, minute, Eng, nine.osf, acircumflex, six.numr, plus, parenright, ibreve, seven.osf, lira, F, I, eogonek, approxequal, eight.osf, Xi, Omacron, C, five.numr, yen, Iogonek.ss01, eng, six, plusminus, i, Umacron, eth, caron, imacron, five, w, Theta, exclam, eta, lslash, iotadieresis, uni047E