Moving executable module symbols parsing to target creation method.

Summary:
In our project we are using remote client-server LLDB configuration.
We want to parse as much debugging symbols as we can before debugger starts attachment to the remote process.
To do that we are passing the path of the local executable module to CreateTarget method at the client.
But, it seems that this method are not parsing the executable module symbols.
To fix this I added PreloadSymbols call for executable module to target creation method.

This patch also fixes a problem where the DynamicLoader would reset a
module when launching the target. We fix it by making sure
Platform::ResolveExecutable returns the module object obtained from the
remote platform.

Reviewed By: labath

Differential Revision: https://reviews.llvm.org/D78654