Apache httpd added HTTP/2 proxy support from 2.4.21 but suggest you run latest (2.4.27 at time of writing) as this module is still changing quite a bit at the moment.
Tomcat has just added HTTP/2 support in Tomcat 9: https://readlearncode.com/configure-tomcat-9-for-http2/
So in theory this should all fit together nicely if you're willing to upgrade to those versions (and install OpenSSL 1.0.2 or above required for HTTP/2).
However, in practice it's still all very new, so bugs are possible. To be perfectly honest, the biggest gains from HTTP/2 are with higher-latency connections like client-to-server. Server-to-server connections like Apache to Tomcat using mod_proxy will see fewer gains.
So, given how new these are, you may wish to just use HTTP/2 on your Apache web server (or any other web server which supports HTTP/2), and use mod_proxy to connect to Tomcat via HTTP/1.1 or AJP. This will give you most of the performance gains of HTTP/2 without the hassle and risk of upgrading everything to get full end-to-end HTTP/2.