[salkinium]

Our Windows CI compiled whatever examples happened to be in its list, so Windows-only bugs in the build system showed up at random whenever the list changed, most recently in #1118. This fixes the ones I found and makes the Windows job compile examples picked for what can actually break there. Turns out it's always one of the same three things, meh.

Requires lbuild v1.23.0 (modm-io/lbuild#88), which returns all relative paths with forward slashes on every host.

• SCons does not preprocess .S files on Windows, since the file system is case-insensitive: the LVGL Helium assembly (Cortex-M55 only) is not copied anymore. RTT was already fixed in Add board connections, hosted configuration and fixes for deduplicated examples #1387.
• Command lines longer than the 8191 characters of cmd.exe: the archive and link commands now use a response file. LVGL alone is about 60000 characters of object files, lol. SCons only writes the file if the command is too long.
• Backslash paths in generated files turning into escape sequences, like generated\nanopb, generated\xpcc and generated\tests: fixed at the source in lbuild instead of in modm, so the minimum lbuild version is now v1.23.0. This removes the modm.windowsify and modm.posixify filters and the escape_level completely, since having to remember them for every single path is what caused these bugs in the first place.
• modm/processing.hpp counted the native path separator to find its headers, which would have left it empty on Windows with the new lbuild, whoops.
• scons compilation_db passed all sources through cmd.exe and failed silently with exit code 0, whoops. The builder is now called without a shell.
• Hosted CMake targets do not create .bin and .hex files anymore, objcopy -Oihex fails on a 64-bit Windows executable.
• The XPCC generator finds its DTD for file:/C:/... paths.
• The generated .gitignore used backslashes, which ignores nothing.
• Git info timestamps fall back to 0 instead of "Unknown" without Git, which did not compile as uint32_t on any OS.
• examples_compile.py also compiles CMake examples on Windows using the "MinGW Makefiles" generator. Make stays excluded, it's documented as unsupported.
• The Windows job compiles an explicit list of examples per failure class: assembly sources, generated paths, long command lines, CMake and CompilationDB, hosted. FreeRTOS and TinyUSB are in there too, but do not reach the limit.
• Tested locally with the CI toolchains and the Windows Python in Wine: all hosted, STM32, AVR and NRF examples of the new list passed with the conversions still in modm. After moving them into lbuild, the nanopb, XPCC, CMake, CompilationDB, image, fiber and hosted examples pass with v1.23.0 and the generated SCons, CMake and OpenOCD files contain no backslashes, while v1.22.0 is rejected.
• The docs test job moved from the container of 2022 to the current one, whose patched DoxyPress finishes again. The old one only has Python 3.8, which cannot install lbuild v1.23.
• CI passed, including the new example list and CMake on the real Windows runner.

Missing: The modm.posixify filter is gone, in case any external repository used it. The Wine container has no Git, so the linux/git example and the hosted unit tests did not run locally and rely on the CI here. The link command limit has no test, since no example has enough source files: I only forced it by lowering MAXLINELENGTH. OpenOCD with forward slashes in its config is reasoned from its startup.tcl, not run.

Conflicts with #1118, which moves all examples and has its own copy of the first two commits. I'll rebase whichever gets merged second.