ab86ac7739 build, qt: Make QWindowsVistaStylePlugin available again (regression) (Hennadii Stepanov)
Pull request description:
This PR is similar to 1be8e0f238, and, actually, it is a #21376 follow up.
Required as in Qt 5.12.x style plugins are separated.
Fixes#22132.
Fixes https://github.com/bitcoin-core/gui/issues/303.
**Note for reviewers**. Besides visual changes in the GUI, you could compare the first dozen of lines in the `debug.log` file.
---
#### Guix build:
```
$ HOSTS=x86_64-w64-mingw32 contrib/guix/guix-build
$ find guix-build-$(git rev-parse --short=12 HEAD)/output/ -type f -print0 | env LC_ALL=C sort -z | xargs -r0 sha256sum
e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855 guix-build-ab86ac7739b2/output/dist-archive/SKIPATTEST.TAG
d3f05888c95d6cf6f4a0bac952d4c0bf1e271f49cb7ab92b08080b753957e5e5 guix-build-ab86ac7739b2/output/dist-archive/bitcoin-ab86ac7739b2.tar.gz
113bb86ffd2854e08d3c0c5cd3f9728f2e4fe6c7a1813bc1c4b73eb48ad6597f guix-build-ab86ac7739b2/output/x86_64-w64-mingw32/bitcoin-ab86ac7739b2-win-unsigned.tar.gz
3fdc99754d6f26d9655a308c8847076d8fd4db8d61f4f18d8ef545894a42c10d guix-build-ab86ac7739b2/output/x86_64-w64-mingw32/bitcoin-ab86ac7739b2-win64-debug.zip
932bb69e3eb1a617f9e337b83220c9d6a277bec421f4d78e32dffde5643eb00c guix-build-ab86ac7739b2/output/x86_64-w64-mingw32/bitcoin-ab86ac7739b2-win64-setup-unsigned.exe
852f4c03ad049fcd6bb2ce25b3bcf4e18b90d34f7232660024b341bd7c8dd710 guix-build-ab86ac7739b2/output/x86_64-w64-mingw32/bitcoin-ab86ac7739b2-win64.zip
c6a33a193a6b128e665198dde94758acab3a5ab7fefe0c3c6617eb98ad01693d guix-build-ab86ac7739b2/output/x86_64-w64-mingw32/inputs.SHA256SUMS
```
ACKs for top commit:
laanwj:
Concept and code review ACK ab86ac7739
fanquake:
ACK ab86ac7739
Tree-SHA512: 9f5498480379fad41de616da48331e123daf5b2294ca79c33ffea2b113b314634be9a2a70bf060cb5be1392a48e9d047891e1d22c129f408f1d76a0bc888441f
6fe012c6bd