[vscode] proposed API evolution between 1.78 and 1.79

[rschnekenbu]

Commit refs for releases:

• 1.78.0: 252e546
• 1.79.0: b380da4

Command line used:

• git difftool -d 252e546..b380da4 -- src/vscode-dts/ on vscode repo
• git submodule foreach "grep -irn enabledApiProposals --include=package.json | cut -d ':' -f 1 | xargs jq --raw-output '{filename: input_filename, enabledApiProposals: .enabledApiProposals}'" on vscode-builtins-extensions

Changes to be verified (builtin extension relying on modified proposed APIs)

• ipynb relies on 2 modified proposed API (documentPaste and dropMetadata)
• vscode-test-resolver relies on 1 modified proposed API (resolvers)
• markdown-language-features relies on 2 modified proposed APIs (documentPaste and dropMetadata), same as ipynb
• github relies on 2 new proposed API (canonicalUriProvider & shareProvider)
• git relies on 1 new proposed API (canonicalUriProvider)

Tasks following proposed API evolution for 1.79

• documentPaste: [vscode][proposed] documentPaste proposed API updates for 1.79 #12633
• dropMetadata: [vscode][proposed] dropMetadata proposed API updates for 1.79 #12632
• canonicalUriProvider & shareProvider: [vscode][proposed] new canonicalURIProvider and shareProvider proposed API for 1.79 #12634
• resolvers: (not created yet, as only used in test currently)