Make provideStatementRange() create a single chunk virtual doc

[DavisVaughan]

Part 2 of the statement range refinement plan

Surgical tweak to provideStatementRange() and virtualDoc() to only make the virtual doc for that chunk, so parse errors in one chunk can't render other chunks useless from a statement range perspective

You also need posit-dev/ark#1030 if you want to test that you can execute code above a parse error within the same chunk, but that isn't critical to the ability to execute code in an arbitrary chunk if one of them has a parse error.

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Before, if you make a typo in one chunk:

• ❌ In the same chunk, can't use statement execution above the typo
• ❌ In the same chunk, can't use statement execution below the typo
• ❌ In any other chunk, can't use statement execution

quarto-before.mov

After, if you make a typo in one chunk:

• ✅ In the same chunk, can use statement execution above the typo (Refine statement range parse error behavior posit-dev/ark#1030)
• ❌ In the same chunk, can't use statement execution below the typo
• ✅ In any other chunk, can use statement execution (this PR)

quarto-after.mov

[juliasilge]

Addresses posit-dev/positron#3233 partially

[juliasilge]

This is working great for me! I reviewed with the current Positron daily so I don't have posit-dev/ark#1030 in it, but the behavior is as expected and looks good.

Before we merge this, can you:

• add a new vdoc.test.ts to the extension tests here with some basic tests of the virtual documents we make with the new options? One option is to make a utility similar to roundtripSnapshotTest() but for virtual docs (one way only, .qmd ➡️ .R or .py) and another option would be to inline the structure of the vdoc in the test file. Take a look at what we have in apps/vscode/src/test/examples and the tests in quartoDoc.test.ts for example on snapshots. Be aware you will not have access to any language pack extension in the tests, only the Quarto extension itself, but I think that will be fine in this case.
• update the copyright year to say "Copyright (C) 2022-2026 by Posit Software, PBC" on the files you edited?