Compatibility map for handling older fonts

[ronaldtse]

From @Dyuzhev:

I've found a strange issue with 'Times New Roman' font from package mscorefonts.
Sometimes the character U+2009 (Thin Space) shows as '#' and in log we have the message:
WARNING: Glyph "?" (0x2009) not available in font "TimesNewRomanPSMT".

But sometimes this character shows ok.
For example, in the document NIST.SP.800-126r3.xml (see issue #17 (comment 315672945)), in Table 12 (ds:component) there are a few characters 0x2009 (before and after dash), but only in second row we have a problem.

When I cut some text from table cell (dateTime -> dateT), then it shows ok:

On my laptop (Win10) there isn't such issue, and all glyph show ok.
Font file information:

• Times.TTF from mscorefonts package: 330 412 bytes, version 2.82
• times.ttf from C:/Windows/Fonts: 1 195 688 bytes, version 7.00

I don't figure out what is the reason of this issue. I see only one solution - replace all U+2009 character into space in xml.

We may have a need for some font symbol mapping for backwards compatibility.

If we decide that the mapping is necessary, we should put this caveat on the Metanorma.com website after PDF functionality is integrated. (and a map of what symbols are mapped to which)