Remove `!` from `Microsoft.Extensions.FileProviders.Physical`

[maxkoshevoi]

Description

This is a blanket issue for all ! operations that were added in #57409
They should be removed or reviewed.

Left to be fixed/reviewed:

• PhysicalFileProvider.FileWatcher LazyInitializer.EnsureInitialized. Possible fix - remove _fileWatcherInitialized field.
• PollingFileChangeToken and PollingWildCardChangeToken IChangeToken.RegisterChangeCallback

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Issue Details

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Description

This is a blanket issue for all ! operations that were added in #57409
They should be removed or reviewed.

Left to be fixed/reviewed:

• PhysicalFileProvider.FileWatcher LazyInitializer.EnsureInitialized. Possible fix - remove _fileWatcherInitialized field.
• PollingFileChangeToken and PollingWildCardChangeToken IChangeToken.RegisterChangeCallback

Author:	maxkoshevoi
Assignees:	-
Labels:	untriaged, area-Extensions-FileSystem
Milestone:	-