feat: gather Flow and Hilla Gradle tasks under vaadin group

[taefi]

Description

This gathers all available Gradle tasks from
Hilla and Flow plugins under one task group
"Vaadin". Also, this gets rid of all the
duplicate extension parameters from
EngineProjectExtension.

The EngineProjectExtension instance that
currently being exposed to users as hilla
can remain the same to show which
parameters are related to which set of tasks,
for example, if the users wants to set the
exposedPackagesToParser, that should
be set via hilla extension:

hilla {
    exposedPackagesToParser =["com.example"]
}

vs. setting the productionMode should be done
via vaadin extension:

vaadin {
    productionMode = true
}

Alse need to decide about which prefix to use
for each set of tasks: hilla for Hilla specific
tasks e.g. hillaGenerate vs. vaadin everywhere
e.g. vaadinGenerate, vaadinConfigure, and etc.

Part of vaadin/platform#4945

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (39f662e) 95.30% compared to head (1c05003) 95.30%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1996   +/-   ##
=======================================
  Coverage   95.30%   95.30%           
=======================================
  Files          52       52           
  Lines        3496     3496           
  Branches      527      527           
=======================================
  Hits         3332     3332           
  Misses        129      129           
  Partials       35       35           

Flag	Coverage Δ
unittests	95.30% <ø> (ø)

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[sonarcloud]

Quality Gate passed

Kudos, no new issues were introduced!

0 New issues
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud

[vaadin-bot]

This ticket/PR has been released with Hilla 24.4.0.alpha3 and is also targeting the upcoming stable 24.4.0 version.