Unfortunately, this patch becomes big because this includes multiple utility
methods to normalize white-spaces and touching a lot of places.
In some edge cases, this starts failing when the new white-space normalizer is
enabled.
```
FAIL execCommand("forwarddelete", false, ""): "a [] | b" - assert_equals: Modified text is wrong expected "a " but got "a "
FAIL execCommand("forwarddelete", false, ""): "a [] | b" - assert_equals: Modified text is wrong expected "a " but got "a "
FAIL execCommand("forwarddelete", false, ""): "a []b| c" - assert_equals: Modified text is wrong expected "a " but got "a "
FAIL execCommand("forwarddelete", false, ""): "a [] <span style=white-space:pre;> </span>" - assert_equals: expected "a <span style=\"white-space:pre;\"> </span>" but got "a <span style=\"white-space:pre;\"> </span>"
```
In these failures, we normalize the trailing white-spaces of the preceding
`Text` too, but Chrome does not do that. However, in some cases, they do
in similar cases. Therefore, it's hard to align all cases due to the handling
order difference. Additionally, these failure results are not odd. So, these
new failures are acceptable.
```
FAIL execCommand("forwarddelete", false, ""): "<span>abc[] <span> def</span></span>" - assert_equals: expected "<span>abc<span> def</span></span>" but got "<span>abc<span> def</span></span>"
FAIL execCommand("forwarddelete", false, ""): "<span><span>abc[] </span> def</span>" - assert_equals: expected "<span><span>abc</span> def</span>" but got "<span><span>abc</span> def</span>"
FAIL execCommand("forwarddelete", false, ""): "<span>abc[] </span><span> def</span>" - assert_equals: expected "<span>abc</span><span> def</span>" but got "<span>abc</span><span> def</span>"
FAIL execCommand("forwarddelete", false, ""): "<span>abc[] </span><span> def</span>" - assert_equals: expected "<span>abc </span><span> def</span>" but got "<span>abc </span><span> def</span>"
```
In these failures, we don't normalize the leading white-spaces of the following
`Text`. However, Chrome does so in some other cases. So, it's hard to align
the behavior in these cases too. The new normalizer ensures that the preceding
`Text` ends with a visible char. Therefore, the following `Text` won't starts
with new invisible white-spaces. Therefore, these failures are also acceptable.
```
FAIL execCommand("forwarddelete", false, ""): "<span style=white-space:pre;> [] </span> a" - assert_equals: expected "<span style=\"white-space:pre;\"> </span> a" but got "<span style=\"white-space:pre;\"> </span> a"
```
In this failure, we don't normalize the following `Text` but Chrome does it.
However, I don't think we should do it because this updates the `Text` which
is preformatted. Therefore, this is also acceptable.
So, I think that we can accept all new failures.
Differential Revision: https://phabricator.services.mozilla.com/D239468
2e3d9fe6d5