A new function IsFileNameValid is added to check if input FileName is valid. If the FileName meets the following scenirio, it will be considered to be invalid:
1) There is two "\" in the path. For example, ".\SomePath\\".
2) There is a least one "/" in the path. The reason is that UEFI 2.1 specifcation only mention that ".", ".." and "\" is valid path modifiers.
3) There is more than two continous dots in the path name token. For example, ".\SomePath\....\SomeName.txt".
git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@4973 6f19259b-4bc3-4df7-8a09-765794883524
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