graphics/mtpaint: update to 3.50.08

[eduardo]

Summary

graphics/mtpaint: update to 3.50.08

- remove USES=tar:bzip2 related to 3.40 distfile tar.bz2
- use ${PREFIX}/share/man for manual pages
- turn on WEBP option by default (forgotten in last update)

Changelog-like descriptions in each commit since 3.50.3 [1].

[1] https://github.com/wjaguar/mtPaint/commits/master

Approved by:	dbaio, garga (mentors)
Differential Revision:	https://reviews.freebsd.org/D29321

Test Plan

$ portlint -C
WARN: Makefile: [65]: possible direct use of command "tr" found. use ${TR} instead.

(line 65, tr is an language in a list)

poudriere testport logs:

114amd64 11.4-RELEASE-p8 amd64
114i386 11.4-RELEASE-p8 i386
122amd64 12.2-RELEASE-p4 amd64
122i386 12.2-RELEASE-p4 i386
140amd64 14.0-CURRENT amd64
140i386 14.0-CURRENT i386

[garga]

pkg-plist

2 ↗

(On Diff #85954)

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[eduardo]

make makeplist instead of manual editing:

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