Fix warnings added in 8d9a0e85bd6ab4fe5268a1d759a787f72ff9333e.
MSVC: Recognize PGFILEDESC in contrib and conversion_procs modules.

Achieve this by consistently using four-argument Solution::AddProject()
calls.  Remove ad hoc Makefile parsing made redundant by doing that.

Michael Paquier and Noah Misch, reviewed by MauMau.
MSVC: Process Makefile line continuations more like "make" does.

Unlike "make" itself, the MSVC build process recognized a continuation
even with whitespace after the backslash.  (Due to a typo, some code
sites accepted the letter "s" instead of whitespace).  Also, it would
consume any number of newlines following a single backslash.  This is
mere cleanup; those behaviors were unlikely to cause bugs.
MSVC: Apply icons to all binaries having them in a MinGW build.
contrib/test_decoding/Makefile sets MODULES, so omit OBJS.

Michael Paquier
Add file version information to most installed Windows binaries.

Prominent binaries already had this metadata.  A handful of minor
binaries, such as pg_regress.exe, still lack it; efforts to eliminate
such exceptions are welcome.

Michael Paquier, reviewed by MauMau.