`WK_CHECKOUT_PATH` defines location of webkit checkout on the
file system. All browser-related scripts, like `prepare_checkout.sh` and
`export.sh` respect this environment variable on all platforms.
**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.
Currently, it might happen that two different patches clash for the
same build number for the browsers. In this case, authors might
not even know that they need to rebaseline.
This patch starts adding a second line to `BUILD_NUMBER` files - the
signature and date of the `BUILD_NUMBER` change. These are guaranteed
to clash, so it should not be possible to land patches without
re-baselining them.
This changes `export.sh` to export diffs instead of patches.
`export.sh` now does not touch working directory, thus not
triggering clean builds and not intefering with an on-going
build.
Turns out `git rmeote get-url` resolves the `insteadOf` substitutions
and ends up with a different URL.
This patch bypasses these substitutions to properly validate
remote url.
