Add missing surround sound identifiers

[messmerd]

This PR adds two missing surround sound identifiers: "Side Left Height" (or top middle left) and "Side Right Height" (or top middle right) as seen in the Dolby 7.1.6 specification which was mentioned in #407.

"Top Center" (CLAP_SURROUND_TC) already exists so I don't think a 3rd identifier is needed.
This addition should be backwards compatible.

As a disclaimer, I do not know anything about surround sound, so someone familiar with it should look over this PR.

Closes #407

[abique]

Thanks!

[abique]

@roelofvkr maybe you want to approve this change?

[roelofvkr]

Thanks for checking! This also looks good to me and the current spec be enough to support up to 9.1.6.

I did see dolby has one more spec for 11.1.8, which would require more additions (it seems like they have another set of rear speakers and another set of top rear/side speakers), but we don't support that and I couldn't really find any other software or plugin format that does.

For me this is good, but I did want to mention the 11.1.8 spec for completeness' sake.

[messmerd]

Do you think any of the identifier comments should be changed? (whether for this PR's additions or older identifiers)

I ask because there are abbreviations like "TSL" which stands for "Top Side Left", but the comment next to it says "Side Left Height". "Top"/"Height" and "Back"/"Rear" are used interchangeably.

[abique]

Do you think any of the identifier comments should be changed? (whether for this PR's additions or older identifiers)

I ask because there are abbreviations like "TSL" which stands for "Top Side Left", but the comment next to it says "Side Left Height". "Top"/"Height" and "Back"/"Rear" are used interchangeably.

I think they should be updated so they include both common descriptions.

[messmerd]

I think they should be updated so they include both common descriptions.

Done

[abique]

Thank you very much, great work :-)