Moves files generated in windows/flutter/ as part of the build to an ephemeral/ subdirectory, matching the approach used on macOS (and in the future, Windows).

Adds that directory to the generated properties file to minimize hard-coding of paths in the project.

When building in profile or release mode on desktop, add a prominent
warning that it's actually a debug build. This is to help address issues
with people being unaware of the current state of builds due to
following third-party guides rather than official documentation.

macOS is not included since PRs are in flight for macOS release support.

This reverts commit bd52a78c.

Move tools tests into a general.shard directory in preparation to changing how we shard tools tests (#36108)

- Adds desktop projects to ApplicationPackageStore
- Plumbs target overrides through the desktop builds

Moves the logic for finding vcvars64.bat to a new VisualStudio class
that encapsulates finding, and providing information about, VisualStudio
installations. Adds a validator for it, and runs it for Windows
workflows in doctor.

Switch from building Runner.vcxproj to Runner.sln on Windows, to allow
for multiple-project builds (e.g., separate plugin projects).

Rather than hard-coding a set of locations to check, use vswhere (which
is installed by VS 2017 and later), and construct the vcvars64.bat path
relative to that. This will allow Windows builds to work without special
configuration for people who have VS installed at a custom path.

Also adds error logging with different messages for each failure point,
so that rather than the not-very-informative 'failed to find
vcvars64.bat' message, the failure will provide feedback about what to
do.

This is an interim solution; later this will be replaced by a
VisualStudio class with associated validator to match the structure of
the other toolchains.

Fixes #33249

Invoking msbuild with runInShell makes handling path escaping more
error-prone, and substantially increases the chances of running into
maximum path limits. This replaces the direct call with a .bat wrapper
that calls vsvars64.bat then msbuild, and uses relative paths within the
script to keep command lengths short.

Fixes https://github.com/flutter/flutter/issues/32792

Eliminates the need for a build.bat in the Windows build workflow, adding
preliminary support for building using msbuild. The handling of
vcvars64.bat may be refined in the future, but this serves as a starting point.

* Re-enable const