Missing FileSystemProvider for the 'jdt' scheme

vscode-java uses a custom URI scheme, jdt, to represent binary class files. However it only provides a TextDocumentProvider so jdt:// URIS can be opened as documents. Because vscode-java doesn't (yet) provide a FileSystem provider, vscode.workspace.fs.readFile calls on jdt URIs throw an ugly exception:

ENOPRO: No file system provider found for resource 'jdt://contents/java.base/java.lang/String.class?%3Ddemogorgon%2F%5C%2FUsers%5C%2Ffbricon%5C%2F.sdkman%5C%2Fcandidates%5C%2Fjava%5C%2F21.0.2-tem%5C%2Flib%5C%2Fjrt-fs.jar%60java.base%3D%2Fjavadoc_location%3D%2Fhttps%3A%5C%2F%5C%2Fdocs.oracle.com%5C%2Fen%5C%2Fjava%5C%2Fjavase%5C%2F21%5C%2Fdocs%5C%2Fapi%5C%2F%3D%2F%3D%2Fmaven.pomderived%3D%2Ftrue%3D%2F%3Cjava.lang%28String.class'

This affects Continue, see https://github.com/continuedev/continue/pull/5536, which also impacts Granite.Code, see https://github.com/Granite-Code/granite-code/issues/115.

vscode-java should provide a proper FileSystemProvider for the jdt scheme.

Start by locating the existing TextDocumentProvider for the jdt URI scheme and trace the vscode.workspace.fs.readFile calls described in the issue. Add the corresponding FileSystemProvider behavior for jdt URIs and verify that those reads no longer throw the reported ENOPRO exception.