Add diagnostics where errors/warnings are emitted

[ralismark]

This is a followup of #625 that adds diagnostics to all places in xetex where errors or warnings are emitted (unless I've missed any). This doesn't add any to bibtex or dpx.

I've mainly looked for places

• which call functions that set history (mainly begin_diagnostic())
• that have the "print file & line number" block which error_here_with_diagnostic replaces
• which call error() and related functions

[codecov]

Codecov Report

Merging #635 into master will decrease coverage by 0.30%.
The diff coverage is 66.21%.

@@            Coverage Diff             @@
##           master     #635      +/-   ##
==========================================
- Coverage   46.13%   45.83%   -0.31%     
==========================================
  Files         138      138              
  Lines       59956    60445     +489     
==========================================
+ Hits        27660    27702      +42     
- Misses      32296    32743     +447     

Impacted Files	Coverage Δ
tectonic/xetex-pic.c	41.49% <0.00%> (+0.70%)	⬆️
tectonic/xetex-ini.c	88.34% <46.66%> (+1.23%)	⬆️
tectonic/xetex-math.c	71.38% <66.66%> (+0.64%)	⬆️
tectonic/xetex-xetex0.c	79.40% <67.23%> (+0.92%)	⬆️
tectonic/xetex-errors.c	50.58% <100.00%> (+1.17%)	⬆️
tectonic/xetex-linebreak.c	84.74% <100.00%> (+0.12%)	⬆️
tectonic/xetex-output.c	82.98% <100.00%> (+0.78%)	⬆️
tectonic/xetex-pagebuilder.c	95.00% <100.00%> (+1.12%)	⬆️
tectonic/xetex-shipout.c	62.64% <100.00%> (-0.02%)	⬇️
src/lib.rs	15.42% <0.00%> (-56.01%)	⬇️
... and 55 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update fe62a31...6110cfd. Read the comment docs.

[pkgw]

Great, thank you for your submission! I look forward to reviewing.

This long weekend I released your first PR in version 0.1.13. I have rebuilt the CI/CD systems and release workflow to be based around a new automation tool that I have spent a long time planning, cranko, so once this PR is merged I plan to get the code released promptly.

(I am fine with ignoring the codecov complaints here, given the nature of the changes.)

[pkgw]

What a tour de force! I tried to read everything over and only spotted one very minor item I'd like to request a change for. Great work!