[mono][aot] Use an mrgctx for all gshared methods on iOS

[kotlarmilos]

This PR enables the use of the MonoMethodRuntimeGenericContext structure for all gshared methods, eliminating the need for generating rgctx fetch trampolines. Preliminary size saving on HelloiOS app is approximately 160kb or -0.646% in release LLVM mode.

HelloiOS .app	Baseline (main branch)	Target (this branch)
HelloiOS	20393904	20186936
Info.plist	982	982
PkgInfo	8	8
Program.aotdata	5888	5952
Program.deps.json	12781	12781
Program.dll	6144	6144
Program.runtimeconfig.json	1064	1064
System.Console.aotdata	2976	3032
System.Console.dll	17408	17408
System.Private.CoreLib.aotdata	679712	703584
System.Private.CoreLib.dll	1158144	1158144
aot-instances.aotdata	531200	554824
icudt.dat	1859648	1859648

Considering potential speed implications of such a change, I suggest merging this PR after the Preview 5 snap.

Fixes #82906

[ghost]

Tagging subscribers to 'os-ios': @steveisok, @akoeplinger
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Issue Details

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This PR enables the use of the MonoMethodRuntimeGenericContext structure for all gshared methods, eliminating the need for generating rgctx fetch trampolines. Preliminary size saving on HelloiOS app is approximately 2kb or -0.646% release LLVM mode.

HelloiOS .app	Baseline (main branch)	Target (this branch)
HelloiOS	20393904	20186936
Info.plist	982	982
PkgInfo	8	8
Program.aotdata	5888	5952
Program.deps.json	12781	12781
Program.dll	6144	6144
Program.runtimeconfig.json	1064	1064
System.Console.aotdata	2976	3032
System.Console.dll	17408	17408
System.Private.CoreLib.aotdata	679712	703584
System.Private.CoreLib.dll	1158144	1158144
aot-instances.aotdata	531200	554824
icudt.dat	1859648	1859648

Considering potential speed implications of such a change, I suggest merging this PR after the Preview 5 snap.

Fixes #82906

Author:	kotlarmilos
Assignees:	kotlarmilos
Labels:	NO-MERGE, area-Codegen-AOT-mono, os-ios, size-reduction
Milestone:	8.0.0