Fix bug when updating data in variable panel.

Grid event naming CHANGE->CHANGING was wrong. CHANGE->CHANGED is the way to go.

SVGHMI: update tests/evghmi to reflect/test latest changes. update generated XSLT.

SVGHMI: multiple non significant changes: doc fixes, modern style access to attributes, enforce double quotes around member name in object literals.

SVGHMI: Changes /CURRENT_PAGE_* behaviour to prevent problem whith multiclient : all clients were switching page when one was jumping.
- now PLC have to prefix page name with "!" to order page switch.
- HMI do not prefix with "!" when jumping, this avoiding looping incidently
- In case of multiple client:
CURRENT_PAGE reflects current page of last client hwo did jump
Setting CURRENT_PAGE with "!" affects all clients simultaneously

SVGHMI: changes that should fix some corner cases about unlinking and discardable element that still didn't show until now.
- list that would have been declared in some groups could have been discarded.
- elements to be unlinked were comuted based on filtering $hmi_elements, whereas $hmi_widget already filtered list

SVGHMI: update generated XSLT

merged

SVGHMI: add CURRENT_PAGE_{location} global variable to reflect currently visible page. If PLC wites some valid page reference in that variable, it triggers page switch. Additionally, fixed /HEARTBEAT being subscribed systematically by JS code even when wtchdog is not enabled.

Follow-up on 83ed4ea362db 'IDE: prevent invoking matiec when IEC code did not change since last build' : build unconditionally after clean

merged

OPC-UA: fix types in model not being preserved after reload of CSV file, leading to exception when changing selection lists content.

OPC-UA: Removed more "LocalizedText()", this time in selected variable list

IDE: prevent invoking matiec when IEC code did not change since last build.

SVGHMI: prevent systematic rebuild when there are multiple instances of SVGHMI CTN.

SVGHMI: optimize HMI tree handling C code to lower CPU usage when traversing large trees