EL: improve resourcebundles handling

[NicolaIsotta]

This is a follow-up to #8603
The main aim is enabling CTRL + Hover and CTRL + click on ResourceBundle items in JSF pages:


The features were already integrated in ELHyperlinkProvider but it seems GsfHyperlinkProvider has the precedence so I had to implement them in ELDeclarationFinder (which is called by GsfHyperlinkProvider).
Aside from that, I tried to improve the resource bundled loading here and there, using the built-in cache whenever possible.
This also includes:

• new svg icons
• declaration popup look improved

[NicolaIsotta]

Updated and squashed, I think this is ready for review

[matthiasblaesing]

I tested this with a minimal JSF project and that worked for me.

Looking through the changes I did not spot obvious problems and just have a minimal nitpick (see inline comment).

I have one more request. I normally would not request via a public forum, but I don't know whether a direct message via email would reach you. Please check your email inbox. There should be two emails with the same text regarding the Apache NetBeans Project (one from my personal email address and one from my @apache.org address), maybe these were lost in the SPAM folder.

[matthiasblaesing]

One thing when I look at the commit, I'd like to ask you to update the commit message with the Intention. I would suggest:

Improve goto declaration for ResourceBundles in JSF files and improve rendering

The goto declaration implementation now does not directly jump to the base 
properties file, but give the use the option to choose the intent property
file also offering the other language files.

Rendering of the popup was updated and svg icons added.

The commit message will be the element that people see in the history, so while the screenshot is very welcome here for illustration, for history the commit message is more important.

[NicolaIsotta]

One thing when I look at the commit, I'd like to ask you to update the commit message with the Intention. I would suggest:

Improve goto declaration for ResourceBundles in JSF files and improve rendering

The goto declaration implementation now does not directly jump to the base 
properties file, but give the use the option to choose the intent property
file also offering the other language files.

Rendering of the popup was updated and svg icons added.

The commit message will be the element that people see in the history, so while the screenshot is very welcome here for illustration, for history the commit message is more important.

I updated the commit message

[NicolaIsotta]

Updated and squashed

[matthiasblaesing]

Thank you!