[vscode] API gap: Theia master vs. VS Code 1.98

[rschnekenbu]

This bug tracks the differences between current master Theia VS Code API and VS Code 1.98.
Based on analysis done in #15129

Public APIs:

• [vscode] API gap: Theia master vs. VS Code 1.97 #14936
• [vscode] Some Selection properties are now readonly (anchor, active, isReversed) #15130
• [vscode] SnippetTextEdit now has an optional keepWhitespace property #15131
• [vscode] SourceControlResourceGroup#contextValue added #15132
• [vscode] Rename AuthenticationForceNewSessionOptions into AuthenticationGetSessionPresentationOptions #15133
• [vscode] Stubbed LanguageModelChatTool inputSchema optional Property can now be also undefined #15134

Declarative APIs:

• Menu search

Proposed API evolution (see #14897):

• [vscode] remove proposed API createFileSystemWatcher #15135
• [vscode] Evolution of the proposed stubbed APIs with vscode 1.98 #15136

Application management:

• [vscode] bump API compatibility version to 1.98.X #15138

[rschnekenbu]

#15265 is not blocking this task, as public apis are supported, and this is only a removal.
The other changes are also non blocking, as they are evolutions on stubs.