devel/electron38: add experimental port of electron 38

Chromium patches obtained from:
FreeBSD ports tree at d7a8c7e76b85da4c340babd701e2e9088568daa9.

Changelog: https://www.electronjs.org/blog/electron-38-0

Author: tagattie

Mk/Uses/electron.mk

@@ -119,7 +119,7 @@ _INCLUDE_USES_ELECTRON_MK=	yes
 # Electron uses Node.js (actually a node package manager) for build
 .include "${USESDIR}/nodejs.mk"
 
-_VALID_ELECTRON_VERSIONS=	6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37
+_VALID_ELECTRON_VERSIONS=	6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38
 _VALID_ELECTRON_FEATURES=	npm appbuilder prefetch extract rebuild build
 _VALID_ELECTRON_FEATURES_NPM=	npm yarn1 yarn2 yarn4 pnpm
 _VALID_ELECTRON_FEATURES_APPBUILDER=release devel