Several metrics issues in Roboto Mono worth fixing together

In [a pull request for a quick fix to the `isFixedPitch` flag of Roboto Mono](https://github.com/google/fonts/pull/1824), I came across a few other bugs. I'm not the first person to notice these, but I wanted to track my notes in an issue, and combine the other issues into this one, as I believe the fixing work should be done together.

Related issues:

- [#142, Roboto mono italics different width](https://github.com/google/fonts/issues/142). This has 10 👍 reactions so far, indicated this as a problem that is affecting a substantial number of users.
- [#249, Roboto Mono regular and italic do not display as the same width](https://github.com/google/fonts/issues/249)
- [#251, Roboto Mono is considered variable-pitch by PuTTY in Windows](https://github.com/google/fonts/issues/251) if it isn't completely solved by PR #1824
- [#1408, Roboto Mono unusable for ASCII art / plain text diagrams ](https://github.com/google/fonts/issues/1408) shows that 1) Roboto Mono has arrows which are the wrong character width and 2) line heights are very different from other Monospace fonts

When there is time for a designer to dedicate to fixing Roboto Mono, they should:

- [ ] ensure that all glyphs – across all styles – have the exact same advance width
- [ ] ensure that vertical metrics are consistent across platforms and relatively similar to other monospace fonts
- [ ] potentially, we could also add box-drawing glyphs to close issue #360, though this would get into glyph extension rather than bug-fixing
- [ ] test that these updates allow Roboto Mono to be used in the Windows Console (see thread for more context)

# Roboto Mono Regular - Fontbakery fails

:fire: FAIL: Checking OS/2 usWinAscent & usWinDescent.

* [com.google.fonts/check/040](https://github.com/googlefonts/fontbakery/search?q=com.google.fonts/check/040)
* :fire: **FAIL** OS/2.usWinAscent value should be equal or greater than 2163, but got 1946 instead [code: ascent]
* :fire: **FAIL** OS/2.usWinDescent value should be equal or greater than 555, but got 512 instead [code: descent]

:fire: FAIL: Checking OS/2 Metrics match hhea Metrics.

* [com.google.fonts/check/042](https://github.com/googlefonts/fontbakery/search?q=com.google.fonts/check/042)
* :fire: **FAIL** OS/2 sTypoAscender and hhea ascent must be equal. [code: ascender]

:fire: FAIL: Checking correctness of monospaced metadata.

* [com.google.fonts/check/033](https://github.com/googlefonts/fontbakery/search?q=com.google.fonts/check/033)
* :fire: **FAIL** On monospaced fonts, the value of OS/2.panose.bProportion must be set to 9 (proportion: monospaced), but got 0 instead. [code: mono-bad-panose-proportion]
* :warning: **WARN** Font is monospaced but 34 glyphs (3.266090297790586%) have a different width. You should check the widths of: ['hyphen', 'f', 'gravecomb', 'acutecomb', 'tildecomb', 'hook', 'uni030F', 'dotbelow', 'uni0483', 'uni0484', 'uni0485', 'uni0486', 'uni0488', 'uni0489', 'at.alt', 'uni00AD', 'Dcroat', 'Eth', 'hbar', 'dcaron', 'lcaron', 'ldot', 'tcaron', 'Epsilontonos', 'Etatonos', 'Iotatonos', 'Omicrontonos', 'Upsilontonos', 'Omegatonos', 'exclamdbl', 'dcroat', 'uni20AB', 'uni049E', 'uni049F'] [code: mono-outliers]

:fire: FAIL: Does the font have a DSIG table?

* [com.google.fonts/check/045](https://github.com/googlefonts/fontbakery/search?q=com.google.fonts/check/045)
* :fire: **FAIL** This font lacks a digital signature (DSIG table). Some applications may require one (even if only a dummy placeholder) in order to work properly.

The most obvious problem for a monospace is that some glyphs are not the standard width – a few are around 8% wider than they should be:



# Roboto Mono Italic

:fire: FAIL: Checking post.italicAngle value.

* [com.google.fonts/check/130](https://github.com/googlefonts/fontbakery/search?q=com.google.fonts/check/130)
* :fire: **FAIL** Font is italic, so post.italicAngle should be non-zero. [code: zero-italic]

:fire: FAIL: Checking OS/2 usWinAscent & usWinDescent.

* [com.google.fonts/check/040](https://github.com/googlefonts/fontbakery/search?q=com.google.fonts/check/040)
* :fire: **FAIL** OS/2.usWinAscent value should be equal or greater than 2163, but got 1946 instead [code: ascent]
* :fire: **FAIL** OS/2.usWinDescent value should be equal or greater than 555, but got 512 instead [code: descent]

:fire: FAIL: Checking OS/2 Metrics match hhea Metrics.

* [com.google.fonts/check/042](https://github.com/googlefonts/fontbakery/search?q=com.google.fonts/check/042)
* :fire: **FAIL** OS/2 sTypoAscender and hhea ascent must be equal. [code: ascender]

:fire: FAIL: Checking correctness of monospaced metadata.

* [com.google.fonts/check/033](https://github.com/googlefonts/fontbakery/search?q=com.google.fonts/check/033)
* :fire: **FAIL** On monospaced fonts, the value of OS/2.panose.bProportion must be set to 9 (proportion: monospaced), but got 0 instead. [code: mono-bad-panose-proportion]
* :warning: **WARN** Font is monospaced but 35 glyphs (3.3621517771373677%) have a different width. You should check the widths of: ['hyphen', 'f', 'gravecomb', 'acutecomb', 'tildecomb', 'hook', 'uni030F', 'dotbelow', 'uni0483', 'uni0484', 'uni0485', 'uni0486', 'uni0488', 'uni0489', 'uniFFFD', 'at.alt', 'uni00AD', 'Dcroat', 'Eth', 'hbar', 'dcaron', 'lcaron', 'ldot', 'tcaron', 'Epsilontonos', 'Etatonos', 'Iotatonos', 'Omicrontonos', 'Upsilontonos', 'Omegatonos', 'exclamdbl', 'dcroat', 'uni20AB', 'uni049E', 'uni049F'] [code: mono-outliers]

:fire: FAIL: Does the font have a DSIG table?

* [com.google.fonts/check/045](https://github.com/googlefonts/fontbakery/search?q=com.google.fonts/check/045)
* :fire: **FAIL** This font lacks a digital signature (DSIG table). Some applications may require one (even if only a dummy placeholder) in order to work properly.

In the Italic, quite a few of the glyphs mentioned (e.g. `/hyphen` are off by just 1 unit (1203 vs the standard 1202). However, quite a few are off by significantly more, which probably isn't killing anyone, but isn't ideal:



Of course, the _most significant_ problem here is that the standard width in the regular is 1229, but the standard width in the italic is 1202. This is about 2.25% different. Here's [a codepen test](https://codepen.io/thundernixon/pen/gqPoKE) showing the effect this has over a line of text:


There are also issues around vertical metrics which probably make display inconsistent between platforms.