Illegal theorem names give a confusing error message

Prerequisites

Please put an X between the brackets as you perform the following steps:

• Check that your issue is not already filed:
  https://github.com/leanprover/lean4/issues
• Reduce the issue to a minimal, self-contained, reproducible test case.
  Avoid dependencies to Mathlib or Batteries.
• Test your test case against the latest nightly release, for example on
  https://live.lean-lang.org/#project=lean-nightly
  (You can also use the settings there to switch to “Lean nightly”)

Description

When accidentally creating a theorem name that starts with a digit, the error messages can be confusing; especially if the name contains an e.

Context

[Broader context that the issue occurred in. If there was any prior discussion on the Lean Zulip, link it here as well.]

Steps to Reproduce

1. Run

theorem 1easy : True := sorry
--            ^ missing exponent digits in scientific literal
theorem 1hard : True := sorry
--     ^ unexpected token; expected identifier

Expected behavior: Both errors appear at the 1 position

Actual behavior: The errors in the comments appear at the marked positions

Versions

[Output of #version or #eval Lean.versionString]
[OS version, if not using live.lean-lang.org.]

Additional Information

[Additional information, configuration or data that might be necessary to reproduce the issue]

Impact

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Run the minimal theorem examples against the latest Lean nightly in live.lean-lang.org and confirm where each diagnostic is reported. Trace the handling of theorem names beginning with digits, then verify that both errors point to the initial 1 position without introducing dependencies on Mathlib or Batteries.