[WinUI] Cache gesture event subscriptions

[MartyIX]

Description of Change

Interops operations on Windows are costly. This PR avoids unsubscribing events that were not subscribed in the first place and thus improving performance.

Speedscope

• Maui.Controls.Sample.Sandbox.exe_20240420_185714.speedscope.json - main
• Maui.Controls.Sample.Sandbox.exe_20240420_185847.speedscope.json - PR

-> 70% improvement for that particular method.

I test with my complex grid sample basically.

Issues Fixed

Contributes to #21787

[dotnet-policy-service[bot]]

Hey there @MartyIX! Thank you so much for your PR! Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

[MartyIX]

@jonathanpeppers would you mind taking a look please?

[MartyIX]

Measurements with commit a5f8d56fb2fe4b820a41de4b01bcd3e91c6d591f addressing https://github.com/dotnet/maui/pull/21959#discussion_r1575352239 by adding SubscriptionFlags

• Maui.Controls.Sample.Sandbox.exe_20240423_100728.speedscope.json - master
• Maui.Controls.Sample.Sandbox.exe_20240423_100904.speedscope.json - PR

[jonathanpeppers]

/azp run

[azure-pipelines[bot]]

Azure Pipelines successfully started running 3 pipeline(s).

[MartyIX]

@rmarinho Could you take a look please?

[MartyIX]

@jfversluis Could you take a look please?

[jfversluis]

@Foda might be the right person here

[MartyIX]

@Foda Could you take a look please?

[MartyIX]

@rmarinho Is it good to be merged or does it need to wait until SR6?

[MartyIX]

@rmarinho Anything else to do here?