NEW Add option to open files in new tab

[Vaadasch]

This is a feature that is recurringly requested along with the modification of "MAIN_DISABLE_FORCE_SAVEAS"

See for exemple :
https://www.dolibarr.org/forum/t/option-to-open-pdf-in-new-window/8389
https://www.dolibarr.org/forum/t/open-links-in-new-tab/14791
https://www.dolibarr.fr/forum/t/ouverture-des-pdf-dans-une-nouvelle-page/30766
https://www.dolibarr.fr/forum/t/pdf-dans-une-autre-fenetre/8058
https://www.dolibarr.fr/forum/t/ouverture-des-pdf/9447

In this PR, it is adding the option "MAIN_FILES_OPEN_NEWTAB" to open most files inside a newtab if it is not empty.

I will update the wiki once/if this PR is merge.

I suggest is to make this behavior as defaut, as it is the main behavior of all the main tools on the web.
In compensation, we could have an option "MAIN_FILES_OPEN_SAMETAB".
But it require consent from the experts who prefer otherwise, because the consensus will be status quo.

[Vaadasch]

I've added the condition on MAIN_DISABLE_FORCE_SAVEAS so those who do not have it won't open a new tab when then have the popup to download the file.

I don't know how to solve the missing check

[Vaadasch]

Thanks @hregis , i hadn't test enough 😞

[eldy]

I don't think we must introduce a second option. Because the feature is dependent on MAIN_DISABLE_FORCE_SAVEAS activation or not, i think it must be a third value of MAIN_DISABLE_FORCE_SAVEAS
MAIN_DISABLE_FORCE_SAVEAS=0 : Default (file is auto downloaded)
MAIN_DISABLE_FORCE_SAVEAS=1 : For to output the file into the browser tab
MAIN_DISABLE_FORCE_SAVEAS=2 : For to output the file into a browser tab open with target_blank

Because having MAIN_DISABLE_FORCE_SAVEAS off and MAIN_FILES_OPEN_SAMETAB on has no sense.
Don't you think so. if you agree, can you simplify the code to just test on MAIN_DISABLE_FORCE_SAVEAS=2 to add the target_blank ?

[Vaadasch]

Of course, you're perfectly right.
It's done