replaced decorate ThemeFilesystemLoader with more efficient Twig\ChainLoader

[Fantus]

Q	A
Branch	1.5
Sylius Version	1.8.5
Bug fix?	yes
New feature?	no
BC breaks?	no
Deprecations?	no
Related tickets	#70
License	MIT

Small fix regarding mentioned performance, for example dev toolbar takes very long to load.

Test results in PROD and NO DEBUG (Not much of a difference):

siege http://127.0.0.1:8081/en_US/ -b -c 20 -t2m --no-parser

NO THEME ACTIVE	Unchanged	Commented	Pull request
Transactions:	3463	5147	3776	hits
Availability:	100	100	100	%
Elapsed time:	299.31	299.73	299.15	secs
Data transferred:	62.63	93.09	68.29	MB
Response time:	1.72	1.16	1.58	secs
Transaction rate:	11.57	17.17	12.62	trans/sec
Throughput:	0.21	0.31	0.23	MB/sec
Concurrency:	19.94	19.95	19.95
Successful transactions:	3463	5147	3776
Failed transactions:	0	0	0
Longest transaction:	4.87	3.28	4.52
Shortest transaction:	0.33	0.22	0.34

Test results in DEV and DEBUG:
Great difference, almost doubled the throughput. Mostly thats because during the Symfony\Bridge\Twig\DataCollector\TwigDataCollector::lateCollect needs to resolve the twig template again and this is now correctly cached.

siege http://127.0.0.1:8081/en_US/ -b -c 10 -t2m --no-parser

Transactions:		76	146	hits
Availability:		100	100	%
Elapsed time:		119.47	119.29	secs
Data transferred:		6.73	12.94
Response time:		14.63	7.97	secs
Transaction rate:		0.64	1.22
Throughput:		0.06	0.11	MB/sec
Concurrency:		9.31	9.75
Successful transactions:		76	146
Failed transactions:		0	0
Longest transaction:		19.74	11.93
Shortest transaction:		1.18	1.21
Shortest transaction:	0.33	0.22	0.34

I also tested it with the sylius bootstrap theme active and it works