**Preamble**
1. We're trying to setup a windows-based github self-hosted runner in the
playwright-internal repo.
1. Commands on Windows are mandated to have total arguments length
less then 32767 characters.
1. On windows, github self-hosted runner framework puts repository
checkout at `c:\w\playwright-internal\playwright-internal`
1. Our scripts create a checkout at
`c:\w\playwright-internal\playwright-internal\browser_patches\firefox\checkout`
1. One of the scripts in Firefox buildsystem tries to execute a command,
passing lots of absolute paths to various webidl's
1. The command fails due to restriction in (2)
**Problem**
Firefox build fails since checkout is deeply nested and hits max arg
size on windows.
**Solution**
This patch introduces a new variable `FF_CHECKOUT_PATH` that is
respected by all browser-related scripts. This way we'll be able
to checkout firefox to `c:\firefox` and avoid hitting long arguments
limit.
The `$PROGRAMFILES` variable is defined per the bitness of the
application: 32-bit shells get `C:\Program Files (x86)`, whereas
64-bit shells get `C:\Program Files`.
Visual Studio, however, has only 32-bit build and is always located in
the `C:\Program Files (x86)` folder.
This patch fixes `//browser_patches/firefox/build.sh` on 64-bit windows
shell.
Otherwise if required version is not installed the build fails with a cryptic message like
`error: toolchain '1.45.0-x86_64-unknown-linux-gnu' does not support components`
Firefox buildchain does not fixate `rust` and `cbindgen` versions,
so we want to fixate them on our end.
A table with matching rust version for every firefox version can
be found at [Rust Update Policy for Firefox](https://wiki.mozilla.org/Rust_Update_Policy_for_Firefox).
Additionally, there are checks in `mozbuild` for the minimum
rust version and minimum `cbindgen` version.
This strictly defines Firefox build folder as `obj-build-playwright`.
Currently, Firefox build folder encodes current Mac OS version including
patch versions, and thus we might end up with multiple different build
folders.
