Allow setting Gradle JVM args in Project.xml #1342

Job	Run time
android	25m 44s
macos	47m 38s
docs	34s
air-samples (4.0.5)	3m 2s
flash-samples	36s
air-samples (4.1.5)	3m 13s
html5-samples	1m 24s
ios	11m 31s
air-samples (4.2.5)	3m 24s
linux	14m 15s
air-samples (4.3.1)	3m 9s
windows	14m 40s
package-haxelib	1m 42s
hashlink-samples (windows-latest)	45s
neko-samples (3.4.7, windows-latest)	44s
hashlink-samples (ubuntu-20.04)	17s
hashlinkc-samples (windows-latest)	1m 42s
neko-samples (3.4.7, ubuntu-20.04)	14s
hashlinkc-samples (ubuntu-20.04)	1m 33s
hashlink-samples (macos-12)	45s
neko-samples (3.4.7, macos-12)	41s
hashlinkc-samples (macos-12)	1m 38s
neko-samples (4.2.5, windows-latest)	42s
neko-samples (4.2.5, ubuntu-20.04)	19s
neko-samples (4.2.5, macos-12)	40s
notify	0s
	2h 20m 52s

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