Use FileOptions.SequentialScan in File.ReadAllBytes

[mcpiroman]

System.IO.File.ReadAllBytesAsync already uses FileOptions.SequentialScan flag when opening a file, but System.IO.File.Read does not:

runtime/src/libraries/System.IO.FileSystem/src/System/IO/File.cs

Line 331 in 52d4d8c

using (FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, bufferSize: 1))

Furthermore, this could be added in ReadAllText and alike, but it would need to be routed through StreamReader and that would probably require public API changes.

[RiskRunner0]

@jkotas Hey is it cool if I pick this up, it doesn't sound like it would be too much work. Pretty new to the .NET Runtime repo though, does this seem like an 'Easy' labeled item, or is the work more substantial than I'm thinking.

[jkotas]

Yep, this one should be pretty easy