Only chmod if the file has been created.

This throws a deprecation warning in XDebug 3.

Closes GH-6324.

Msan is missing interceptors for some functions that result in
false positives.

This was part of the removed HTML functionality.

Closes GH-6016.

Mentioned in https://github.com/php/php-src/pull/5965#discussion_r467621123

This PR proposes 3 lines of context so the impact can be seen in tests.
Other `diff` programs show around 3 lines of context.
(This helps indicate exactly which position a test should be updated
to add a new expected line at)

Use the mapping for choosing order to display diffs

Properly include context in cases where the expected output had more lines than
the actual output, e.g.

```
--FILE--
A
A1
A
C
NEARBY
--EXPECTF--
A
B
A1
B
A
B
A
B
NEARBY
```

Closes GH-5968

Don't add colors to the saved `.diff` file.

Related to a41cf3e1d2ed3ae38ad6115a8b65e5f14dae0b49

And add a --color option for run-tests.php

See https://no-color.org/

> an informal standard is hereby proposed:
>
> All command-line software which outputs text with ANSI color added should check
> for the presence of a `NO_COLOR` environment variable that, when present
> (regardless of its value), prevents the addition of ANSI color.

This reverts commit 58489bd3b93e10c150933eefac05297b48213eb3.

This also uses ANSI escape code coloring for .diff files, where it
is not meaningful.

This uses green for lines with `+` and red for lines with `-`.

Colors(Red and Green) would make the failure causes stand out visually when scrolling through errors.

Closes GH-5965