[Swift] Allow swift bridging header import files when reference from current library.

Created by: zayhero-zz

Right now when buck building swift with bridging header, it is not able to import header files when it reference from current library.

For example, in build rule with this setup

apple_library(
    name = 'Greeter',
    bridging_header = 'bridging-header.h',
    headers = glob([
        '*.h',
    ]),
    srcs = glob([
        '*.m',
        '*.swift',
    ]),
    frameworks = [
        '$SDKROOT/System/Library/Frameworks/Foundation.framework'
    ],
)

We can not do #import <Greeter/Greeter.h> in bridging header.

After investigation, I figure its due to buck didn't include the header map generated for current library in SwiftCompile.

This PR is to improve buck so it can support above use case.