Brand new search bar active layer feature matching functionality + UI/UX improvements

[nirvn]

This PR adds a new functionality to the search bar: an active layer feature matching. To begin with, here's a screencast showcasing the UI/UX:

Screencast.from.2023-09-01.11-07-04.webm

Few notes:

• The search functionality must be activated via its f prefix as the search can be quite costly;
• Contrary to the all features (within all layers) search, this search functionality allows for single character searches (thanks to it being prefixed), and will not only try to match against a feature's display name but also all text and numerical fields;
• When an attribute match occurs, the attribute value and attribute name are highlighted, while the feature display name is appended as a second text row (seen in screencast above);
• It is possible to restrict to search to one specific field by using the following syntax: 'f @ATTRIBUTE_NAME search term'). This matches the behavior found in QGIS and can be super useful in narrowing searches on the spot.

The screencast also shows a nice UX improvements added here. Since we are now having quite a few search functionalities, with a few activated only via prefix, it has become slightly harder for QField users to be made aware of all of the cool stuff the search bar those. To remedy to that, the search bar now shows a list of functionalities when users activate the search bar prior to entering text.

Part of the code logic was taken from @nyalldawson 's equivalent locator filter in QGIS (https://github.com/qgis/QGIS/blob/master/src/app/locator/qgsactivelayerfeatureslocatorfilter.cpp). Insuring that QField and QGIS have matching behaviors was important. I'm pretty sure we'll get a few QField users aware of the @ATTRIBUTE restriction in QGIS now ;-P

[qfield-fairy]

🎉 Ta-daaa, freshly created APKs are available for 45a7bf1: arm64-android

Other architectures

• arm-neon-android
• x64-android
• x86-android
• all access arm64-android
• all access arm-neon-android
• all access x64-android
• all access x86-android

[suricactus]

Code looks good.

Needs a bit of docs here and there.

Also put some braces ( for single line ifs. They are okayish if they are followed by return, break or continue, but become super confusing with other statements and error prone when refactoring.

IMO we should add this as a rule to the linter. Opinions @nirvn @m-kuhn ?

[suricactus]

Suggested change

	QStringList prepare( const QString &string, const QgsLocatorContext &locatorContext ) override;
	void fetchResults( const QString &string, const QgsLocatorContext &context, QgsFeedback *feedback ) override;
	void triggerResult( const QgsLocatorResult &result ) override;
	void triggerResultFromAction( const QgsLocatorResult &result, const int actionId ) override;
	QStringList prepare( const QString &string, const QgsLocatorContext &locatorContext ) override;
	void fetchResults( const QString &string, const QgsLocatorContext &context, QgsFeedback *feedback ) override;
	void triggerResult( const QgsLocatorResult &result ) override;
	void triggerResultFromAction( const QgsLocatorResult &result, const int actionId ) override;

A bit of docs would be nice.

[nirvn]

@suricactus , doc available in the parent class: https://api.qgis.org/api/classQgsLocatorFilter.html

[nirvn]

@suricactus , review addressed, thanks a bunch for looking over this.