..and add new definitions isomorphic to xml-light's, but with
Text instead of String. This allows us to keep most of the code in
existing readers that use xml-light, but avoid lots of unnecessary
allocation.
We also add versions of the functions from xml-light's
Text.XML.Light.Output and Text.XML.Light.Proc that operate
on our modified XML types, and functions that convert
xml-light types to our types (since some of our dependencies,
like texmath, use xml-light).
Update golden tests for docx and pptx.
OOXML test: Use `showContent` instead of `ppContent` in `displayDiff`.
Docx: Do a manual traversal to unwrap sdt and smartTag.
This is faster, and needed to pass the tests.
Benchmarks:
A = prior to 8ca191604d (Feb 8)
B = as of 8ca191604d (Feb 8)
C = this commit
| Reader | A | B | C |
| ------- | ----- | ------ | ----- |
| docbook | 18 ms | 12 ms | 10 ms |
| opml | 65 ms | 62 ms | 35 ms |
| jats | 15 ms | 11 ms | 9 ms |
| docx | 72 ms | 69 ms | 44 ms |
| odt | 78 ms | 41 ms | 28 ms |
| epub | 64 ms | 61 ms | 56 ms |
| fb2 | 14 ms | 5 ms | 4 ms |
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