tests: windows: add various llb.AddMount related tests

- [x] testCacheExportCacheKeyLoop
- [x] testOCILayoutSource
- [x] testBuildMultiMount
- [x] testTarExporterSymlink
- [x] testCacheExportIgnoreError
- [x] testBasicCacheImportExport
- [x] testUncompressedLocalCacheImportExport
- [ ] testUncompressedRegistryCacheImportExport (skipped, registry
  setup issues)
- [x] testImageManifestRegistryCacheImportExport
- [ ] testBasicRegistryCacheImportExport (skipped, registry setup
  issues)
- [ ] testMultipleRegistryCacheImportExport (skipped, reg issues)
- [x] testBasicLocalCacheImportExport
- [x] testBasicInlineCacheImportExport
- [x] testRegistryEmptyCacheExport
- [x] testCachedMounts
- [x] testDuplicateCacheMount
- [x] testRunCacheWithMounts
- [-] testDuplicateWhiteouts (d1 white-out TBD)
- [-] testWhiteoutParentDir (some missing white-out details)
- [-] testMoveParentDir (to revisit)
- [x] testMountWithNoSource
- [x] testProxyEnv
- [x] testRelativeMountpoint
- [x] testPullWithLayerLimit
- [x] testValidateDigestOrigin
- [x] testExportAnnotations
- [x] testExportAnnotationsMediaTypes
- [x] testAttestationDefaultSubject
- [x] testAttestationBundle
- [x] testLLBMountPerformance
- [x] testLayerLimitOnMounts

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