tests: add more integration tests for windows/wcow

As a follow up of moby#5027, we will be adding more tests in batches
of 10-15, to bring the coverage at par with Linux where applicable.

Tests completed in `frontend/dockerfile`:
- [x] `testTarExporterBasic`
- [x] `testWorkdirCreatesDir`
- [x] `testCacheReleased`
- [x] `testSymlinkedDockerfile`
- [x] `testMultiArgs`
- [x] `testContextChangeDirToFile`
- [x] `testNoSnapshotLeak`
- [x] `testCopyFollowAllSymlinks`
- [x] `testCopySymlinks`
- [x] `testHTTPDockerfile`
- [x] `testCmdShell`
- [x] `testInvalidJSONCommands` (flaky on Win11/client SKUs
	due to port detection for registry.exe server)
- [x] `testGlobalArg`
- [x] `testCopyOverrideFiles`
- [x] `testCopyVarSubstitution`
- [x] `testCopyWildcards`

Signed-off-by: Anthony Nandaa <[email protected]>

Author: profnandaa