build: fix MSVC UWP builds

The MSVC UWP job in CI did not actually enable UWP. Fix this and
the fallouts discovered after enabling it.

- GHA/windows: make sure to enable UWP in MSVC vcpkg UWP job.
  Use the CMake options and C flags already used for mingw-w64, but use
  `WINAPI_FAMILY_PC_APP` instead of the deprecated `WINAPI_FAMILY_APP`.
  (The former is not supported by mingw-w64, so leave it there as-is.)
  Follow-up to cb22cfca69 #14077

- GHA/windows: by default the MSVC UWP job became 2x-3x slower than
  others after actually enabling UWP. Most of it is caused by
  CMake/MSBuild automatically building full APPX containers for each
  `.exe` target. This includes 21 CMake feature detections. Each
  detection app is built into a 15MB APPX project, with code signing,
  logos, etc. Example:
    https://github.com/curl/curl/actions/runs/12056968170/job/33620610958
  Disable this overhead for curl build targets via custom
  `CMAKE_VS_GLOBALS` options. I've found no way to apply them to feature
  detection targets, so those remain slow.

- cmake: automatically enable Unicode for UWP builds. It's required.
  Also stop enabling it manually in the existing CI job.

- tests: fix `getpid()` use for Windows UWP:
  ```
  tests\server\util.c(281,21): warning C4013: 'getpid' undefined; assuming extern returning int
  ```
  Ref: https://github.com/curl/curl/actions/runs/12061215311/job/33632904249#step:11:38

- src/tool_doswin: disable `GetLoadedModulePaths()` for UWP.
  mingw-w64 UWP was okay with this, but MS SDK headers are not.
  This makes `--dump-module-paths` return empty for UWP builds.
  ```
  src\tool_doswin.c(620,3): error C2065: 'MODULEENTRY32': undeclared identifier
  src\tool_doswin.c(626,11): warning C4013: 'CreateToolhelp32Snapshot' undefined; assuming extern returning int
  src\tool_doswin.c(626,36): error C2065: 'TH32CS_SNAPMODULE': undeclared identifier
  src\tool_doswin.c(632,7): warning C4013: 'Module32First' undefined; assuming extern returning int
  ```
  Ref: https://github.com/curl/curl/actions/runs/12055081933/job/33614629930#step:9:35

- examples: fix `websocket.c` to include `winsock2.h` before `windows.h`
  to make it build with MSVC UWP:
  ```
  include\curl\curl.h(143,16): error C2061: syntax error: identifier 'curl_socket_t'
  include\curl\curl.h(143,16): error C2059: syntax error: ';'
  include\curl\curl.h(417,52): error C2146: syntax error: missing ')' before identifier 'curlfd'
  include\curl\curl.h(417,38): error C2081: 'curl_socket_t': name in formal parameter list illegal
  ```
  Ref: https://github.com/curl/curl/actions/runs/12055317910/job/33615644427#step:14:126

- GHA/windows: silence linker warning with MSVC UWP builds:
  ```
  LINK : warning LNK4075: ignoring '/INCREMENTAL' due to '/OPT:ICF' specification
  ```
  Ref: https://github.com/curl/curl/actions/runs/12055696808/job/33616629610#step:11:38

- GHA/windows: set `/INCREMENTAL:NO` for all MSVC jobs to improve
  performance a little.

- cmake: show `UWP` platform flag.

Ref: #15652
Closes #15657

docs/examples/websocket.c

@@ -28,6 +28,7 @@
 #include <stdio.h>
 #include <string.h>
 #ifdef _WIN32
+#include <winsock2.h>
 #include <windows.h>
 #define sleep(s) Sleep((DWORD)(s))
 #else