Add "-nocygwin" and "USE_CYGWIN" properties to build.ps1 and build.gradle

The tools\scripts\build.ps1 powershell build script for
performing local Windows development builds uses the choco
package manager to install Cygwin. Since media and webkit
modules are skipped the only place Cygwin is actually used
is one call to a "chmod" binary. From my testing it appears
the build and tests complete without this "chmod" call.

Installing all of Cygwin onto a developer's computer to
build OpenJFX is not ideal. Therefore we introduce an argument
to the build script "-nocygwin" which is set to "false" by
default (when the flag is not present in the command-line
invocation of build.ps1). If the flag is set then we set
the -PUSE_CYGWIN gradle property to "false" (a new flag
which defaults to "true") which, when set, skips the call
to "chmod".

TLDR: Add "-nocygwin" command-line argument flag to
tools\scripts\build.ps1 to skip installation of Cygwin.
"-nocygwin" flag sets gradle property "USE_CYGWIN".