Based on the discussion in
https://forum.syncthing.net/t/towards-syncthing-2-0/24072/35 This PR
adds the ability for Windows users to use the pipe character (|) to
escape the metacharacters *, ?, [, and { in .stignore files.
Additionally, this PR adds the ability for the user to set the escape
character to backslash, or any character they want, by adding a line in
the form:
#escape=X
(where X is any single rune), to the top of an .stignore file.
This would allow users to use the same .stignore file across platforms,
by simply adding
#escape=\
to the top of the file.
### Testing
All tests pass in CI.
### Documentation
See https://github.com/syncthing/docs/pull/919Fixes#10057: Support escaping in .stignore files on Windows
Fixes#7547: Ignore pattern with \[ and \] does not work
### Purpose
Locally, on Windows 11, and on the windows-2025 GitHub runner (go 1.23
and 1.24), the `TestCopyRange` test is failing with `The request is not
supported.`
On windows-2022 and windows-2019:
```go
err == syscall.ENOTSUP
```
worked, but on Windows 11 and windows-2025, we need:
```go
errors.Is(err, errors.ErrUnsupported)
```
### Testing
Tested on Windows 11, windows-2019, windows-2022, and
[windows-2025](https://github.com/rasa/syncthing/actions/runs/15525123437/job/43703630634#step:7:2811).
This allows users to easily disable nightly builds in their forks,
simply by disabling the
build-nightly action.
### Testing
I tested it in my fork, and it works.
### Purpose
This fixes#9775. I also improved the comments as they were lacking.
My apologies for introducing this bug. In summary, the bug was
```
mode = mode ^ (ModeSymlink | ModeIrregular)
```
didn't correctly reset those bits. This correctly resets them:
```
mode = mode &^ ModeSymlink &^ ModeIrregular
```
Tested and working in Windows 11 version 10.0.22631.4317. I didn't test
in other versions, but I'm sure this is the only issue.
Ross Smith II
