fix(react): respect tsconfig jsxImportSource (fix #1448)

[cpruijsen]

Description

Fixes #1448.

react({ compiler: true }) lowers JSX in vite:react-compiler with oxc-transform-react. That transform defaults jsx.importSource to "react" when the option is unset. Vite's oxc transform never sees the original JSX, so the per-file tsconfig inference restored in #726 does not apply.

With no plugin-level jsxImportSource, the compiler transform now reads compilerOptions.jsxImportSource from the file's tsconfig using the same resolveTsconfig Vite uses for oxc JSX. An explicit jsxImportSource option still overrides every file.

Reproduction from the issue (two TSX files, no pragmas):

Plugin options	file with jsxImportSource: "@emotion/react"	default React file
{ compiler: false }	@emotion/react/jsx-runtime	react/jsx-runtime
{ compiler: true } (before)	react/jsx-runtime	react/jsx-runtime
{ compiler: true } (after)	@emotion/react/jsx-runtime	react/jsx-runtime
{ compiler: true, jsxImportSource: "@emotion/react" }	@emotion/react/jsx-runtime	@emotion/react/jsx-runtime

What I chose: fill jsx.importSource from the file's tsconfig inside the compiler plugin.

Alternative: set jsx: "preserve" in the compiler plugin so Vite's oxc transform keeps owning JSX, Fast Refresh, and tsconfig inference.

Why: #1419 put JSX and Fast Refresh in the compiler plugin so the compiler sees the original AST. This change only supplies the missing import source and stays reversible. Happy to switch to preserve-JSX if that is preferred.

resolveTsconfig is a hidden rolldown export currently used by Vite. It is loaded through Vite's installation so this package does not gain a new runtime dependency. If you would rather have a public Vite helper, this call site is the consumer.

Checklist

• Read the Contributing Guidelines.
• Check that there isn't already a PR that solves the problem the same way.
• Documentation already states that jsxImportSource is inferred from tsconfig; no extra docs.
• Tests fail without this change and pass with it (packages/plugin-react unit tests).

[doctor8296]

The initial per-file jsxImportSource case works, but the new TsconfigCache becomes stale in a running dev server.
Tested 3beee4f with Vite 8.2.2, Rolldown 1.2.6 and oxc-transform-react 0.147.0:

1. Start Vite with react({ compiler: true }), no global override, and tsconfig pointing to runtime A.
2. Change jsxImportSource to runtime B. Vite detects the change and sends full-reload, but subsequent HTTP responses still import A.
3. Edit the component: the response contains the updated code, but still imports A. Removing jsxImportSource also leaves A instead of reverting to React.

With compiler: false, the same test correctly switches A → B → React. Adding only tsconfigCache?.clear() before the new resolveTsconfig call also makes the native-compiler test pass. This isolates the problem to the cache introduced here, rather than stale HTTP/module responses.
Could you invalidate this cache on relevant tsconfig changes and add a dev-server regression test? Clearing it on every transform is a diagnostic control, but not sure if it solves bug correctly.