…re parsed

The default setting is 'auto', where JSX containing files under react-jsx and react-jsxdev are
always parsed as modules, and esm-format files under module: node12+ are always parsed as modules,
in addition to the 'legacy' detection mode's conditions for other files. (Declaration files are exempt from
these new conditions)

The 'legacy' mode preserves TS's behavior prior to the introduction of this flag - a file is
parsed as a module if it contains an import, export, or import.meta expression.

In addition, there is a 'force' mode that forces all non-declaration files to be parsed as modules.
(Declaration files are still only modules if they contain a top-level import or export.)

This technically breaks the parser API, but it's kinda-sorta backwards compatible so long
as you don't need the functionality associated with more recent compiler flags.