Adding static transform listener

[ayrton04]

Addressses #662.

I went with @clalancette's suggestion and just added a static_only parameter (with a default of false) to the constructors and the init method.

However, that made things slightly awkward, for two reasons:

1. In order to specify static_only, we have to now specify a ton of other optional parameters.
2. If we are setting static_only to true, we now have to specify parameters for the behaviour of the dynamic transform subscriber, even though it won't be used. That felt clunky.

So in addition to the above, I also created a "convenience" class, StaticTransformListener. It inherits from TransformListener and has equivalent constructors (but without the dynamic subscriber parameters). It simply calls the base TransformListener constructor with the required parameters, using dummy values for the dynamic transform subscriber options and QoS.

In addition, I added tests:

1. I added tests that were exactly equivalent to the TransformListener tests, which seem largely aimed at just constructing listeners, rather than using them.
2. I added a new test that has a TransformListener and a StaticTransformListener. We publish dynamic and static transforms, and then check to see if the respective dynamic and static buffers have the transforms we expect.

[ahcorde]

• Linux
• Linux-aarch64
• Windows

[ahcorde]

@clalancette any comments on this one ?

[sloretz]

@clalancette friendly ping 🧇

[ahcorde]

@clalancette do you mind to take a look ?

[ahcorde]

friendly ping @clalancette

[ayrton04]

Hello! Not wanting to be difficult at all, but as we're approaching the 3-month mark for this PR, it would be really great if we could either approve it or reject it. If we're not happy with the overall implementation, I am happy to change it (or just close the PR, if we feel this changes too much).

Thanks!

[ahcorde]

friendly ping @clalancette

[ahcorde]

• Linux
• Linux-aarch64
• Linux-rhel
• Windows