fix(esm-shim): do not insert shims at `import` literal

[younggglcy]

Rollup Plugin Name: @rollup/plugin-esm-shim

This PR contains:

• [x] bugfix
• [ ] feature
• [ ] refactor
• [ ] documentation
• [ ] other

Are tests included?

• [x] yes (bugfixes and features will not be merged without tests)
• [ ] no

Breaking Changes?

• [ ] yes (breaking changes will not be merged unless absolutely necessary)
• [x] no

If yes, then include "BREAKING CHANGES:" in the first commit message body, followed by a description of what is breaking.

List any relevant issue numbers:

resolves #1649

Description

See the repro #1649 given, the shims were inserted into wrong position because the object

{
  keyword: ' import',
  dn: '',
};

matches the ESMStaticImportRegex regex.

This PR fixes it by disallowing \n in the specifier group in the regex.

[tada5hi]

looking good

[younggglcy]

ping politely here. can anyone help merge this pr