build.py: improve BuildTarget error message

Improve the error message when a build target is assigned as dependency
of another build target, which allows to better pinpoint where the issue
lies on.

In the example that follow, modules/meson.build:294 is in a for loop
creating library targets from an array of dictionary, and doesn't point
to the location where interop_sw_plugin is assigned with vlc_opengl:

Before:

    modules/meson.build:294:17: ERROR: Tried to use a build target as a dependency.
    You probably should put it in link_with instead.

After:

    modules/meson.build:294:17: ERROR: Tried to use a build target vlc_opengl as a dependency of target interop_sw_plugin.
    You probably should put it in link_with instead.

It would probably be best to directly pinpoint where the assignment was
made but it's probably harder so start simple by saying what is
concerned by the error.

mesonbuild/build.py

@@ -1346,8 +1346,8 @@ class BuildTarget(Target):
                     self.process_sourcelist(dep.get_sources())
                 self.add_deps(dep.ext_deps)
             elif isinstance(dep, BuildTarget):
-                raise InvalidArguments('''Tried to use a build target as a dependency.
-You probably should put it in link_with instead.''')
+                raise InvalidArguments(f'Tried to use a build target {dep.name} as a dependency of target {self.name}.\n'
+                                       'You probably should put it in link_with instead.')
             else:
                 # This is a bit of a hack. We do not want Build to know anything
                 # about the interpreter so we can't import it and use isinstance.