font-ibm-plex-ttf: update to 6.0.0.

[kkga]

General

• This is a new package and it conforms to the quality requirements

Have the results of the proposed changes been tested?

• I use the packages affected by the proposed changes on a regular basis and confirm this PR works for me
• I generally don't use the affected packages but briefly tested this PR

[ericonr]

Note: this is a major release due to the change in postscript naming structure. Each font now uses abbreviations for Semibold, ExtraLight and Medium (SmBld, ExtLt, and Medm respectively).

Do you use any of the variants? Has software managed to find them correctly?

[kkga]

Good question.

I don't use any specific variants, but judging from fc-match, there might be problems:

> fc-match 'IBM Plex Sans SmBld'   
IBMPlexSans-SemiBold.ttf: "IBM Plex Sans" "SemiBold"

> fc-match 'IBM Plex Sans SemiBold'
Inter-V.ttf: "Inter V" "Regular"