module: fix --check on ambiguous ESM files

[bitpshr]

Fixes #65202. node --check exits 0 on a .js file that contains module syntax and a genuine syntax error, when the file's format is ambiguous (no "type" in the nearest package.json).

Such a file has no format of its own, and defaultGetFormat() reports it as null. checkSyntax() passed that null straight to wrapSafe(), which parses as CommonJS; the module syntax makes that parse bail out before the rest of the file is parsed, so nothing was reported.

At load time the goal for an ambiguous file is decided by looking for module syntax in the source, so this decides it the same way before choosing how to parse.

$ node --check broken.js ; echo "exit: $?"    # import + `var = ;`
exit: 0                                        # before
...
SyntaxError: Unexpected token '='              # after
exit: 1

Verified against a local build. Files whose format is known are unaffected, and ambiguous files without module syntax still parse as CommonJS, so sloppy-mode sources keep working:

case	before	after
.js ambiguous + module syntax + error	exit 0	exit 1
.js ambiguous, sloppy-mode with	exit 0	exit 0
.js ambiguous, plain syntax error	exit 1	exit 1
.mjs, or "type" set	exit 1	exit 1
.js ambiguous, valid ESM	exit 0	exit 0

The added fixture fails the existing test-cli-syntax-bad assertions before this change and passes after. All test-cli-syntax* suites pass locally.

Fixes: #65202

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.32%. Comparing base (4a5eb1c) to head (3b17952).
⚠️ Report is 250 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #65203      +/-   ##
==========================================
+ Coverage   90.15%   90.32%   +0.16%     
==========================================
  Files         744      760      +16     
  Lines      242517   248538    +6021     
  Branches    45688    46893    +1205     
==========================================
+ Hits       218642   224482    +5840     
- Misses      15358    15460     +102     
- Partials     8517     8596      +79     

Files with missing lines	Coverage Δ
lib/internal/main/check_syntax.js	100.00% <100.00%> (ø)

... and 188 files with indirect coverage changes

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