module: derive builtinModules from enabled builtin set

[sjungwon03]

Module.builtinModules is expected to contain only builtins accessible
to user code.

During pre-execution, each experimental flag determines whether its
builtin is added to BuiltinModule's user-requirable set via
BuiltinModule.allowRequireByUsers().

Before this change, getAllBuiltinModuleIds() added every scheme-only
builtin to the Module.builtinModules candidate list, including
experimental builtins that had not been added to the user-requirable
set. initializeCJS() then repeated the flag checks and removed
node:dtls, node:quic, node:ffi, and node:vfs.

Derive the scheme-only portion of Module.builtinModules from the
already-established user-requirable set instead. This keeps the list
consistent with the existing require('node:...') access policy and
removes the duplicated filtering in initializeCJS().

Existing scheme-only builtins such as node:test, node:sea, and
node:sqlite remain listed.

Add coverage for Module.builtinModules and require('node:...')
with and without each experimental flag.

Refs: #56185
Refs: #56870
Refs: #63158

[nodejs-github-bot]

Review requested:

• @nodejs/loaders
• @nodejs/startup

[sjungwon03]

Follow-up: the focused test assumed that node:sqlite is available in
all builds. Slim builds can be compiled without SQLite, so the test now
only verifies node:sqlite when common.hasSQLite is true.

node:test and node:sea remain covered unconditionally.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.12%. Comparing base (55e4ca3) to head (79ffed7).
⚠️ Report is 14 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #65418      +/-   ##
==========================================
- Coverage   90.14%   90.12%   -0.02%     
==========================================
  Files         752      752              
  Lines      251870   252321     +451     
  Branches    47365    47441      +76     
==========================================
+ Hits       227037   227404     +367     
- Misses      16177    16216      +39     
- Partials     8656     8701      +45     

Files with missing lines	Coverage Δ
lib/internal/bootstrap/realm.js	96.36% <100.00%> (+0.06%)	⬆️
lib/internal/modules/cjs/loader.js	98.22% <100.00%> (+0.07%)	⬆️

... and 58 files with indirect coverage changes

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