fix: Add logics to skip non-managed assembly

[filzrev]

This PR intended to fix issue #10682
By adding logic to skip non-managed assembly (that returns false for PEReader::HasMetadata)

PEReader instance creation is relatively heavy operation. (It takes 100ms-500ms)
So created PEReader instance is passed as argument. and reused for subsequent processing.

Note:
referenced native assembly skip logic is not currently implemented.
Because it's rare use case, directly referencing native-assembly (With <Reference> tan and HintPath`)

https://github.com/filzrev/docfx/blob/39c67026fd56cd53c0582740d7a912507dff62ca/src/Docfx.Dotnet/CompilationHelper.cs#L212-L216

[yufeih]

Thank you @filzrev