This fixes Microsoft Edge crashing if someone tries to open or save a file via the file picker. For example, to debug the functionality, I went to:
```
https://drive.google.com -> New -> File upload
```
This used to crash with the following error:
```
[...]
(microsoft-edge:22536): GLib-GIO-ERROR **: 11:11:46.555: No GSettings schemas are installed on the system
[0302/111146.559740:ERROR:elf_dynamic_array_reader.h(64)] tag not found
[0302/111146.559913:ERROR:process_memory_range.cc(75)] read out of range
[0302/111146.568118:ERROR:watson_metadata.cc(170)] unexpected header
Trace/breakpoint trap (core dumped)
```
This PR fixes this error by explicitly making `gsettings-schemas` from
`gtk` available to `microsoft-edge` via `XDG_DATA_DIRS`.
Furthermore, this PR fixes some broken `subsituteInPlace` commands.
Thanks to Jona Enzinger (`@JonaEnz`) who noticed that `--replace
"''${XDG...` should be written as `--replace "\''${XDG...`.
