[gjs] Fix bug with regex issues when parsing GLIMMER_TEMPLATE

[hmajoros]

another specific fix from #1659: when a lint error lands on the line containing <template>, we get an error like the following:

SyntaxError: Invalid regular expression: /\b[__GLIMMER_TEMPLATE(`\b/: Unterminated character class
        at new RegExp (<anonymous>)

an easy way to repro this is to enable the lines-between-class-members rule, and put a <template> immediately after another class member.

I wrote a test, which currently is failing with the following message. This should just need some regexp escaping like Krystan mentioned in the original issue. will work on that shortly

 template tag failing test repro
    ✕ should break (12 ms)

  ● template tag failing test repro › should break

    SyntaxError: Invalid regular expression: /\b[__GLIMMER_TEMPLATE(`\b/: Unterminated character class
        at new RegExp (<anonymous>)

      123 |
      124 |     for (const [index, line] of originalLines.entries()) {
    > 125 |       const column = line.search(new RegExp(`\\b${token}\\b`));
          |                                  ^
      126 |       if (column > -1) {
      127 |         originalLineNumber = index + 1;
      128 |         originalColumnNumber = column + 1;

      at lib/preprocessors/glimmer.js:125:34
          at Array.map (<anonymous>)
      at map (lib/preprocessors/glimmer.js:106:20)
      at Linter._verifyWithProcessor (node_modules/eslint/lib/linter/linter.js:1906:16)
      at Linter._verifyWithConfigArray (node_modules/eslint/lib/linter/linter.js:1765:25)
      at Linter.verify (node_modules/eslint/lib/linter/linter.js:1479:65)
      at Linter.verifyAndFix (node_modules/eslint/lib/linter/linter.js:2031:29)
      at verifyText (node_modules/eslint/lib/cli-engine/cli-engine.js:245:48)
      at CLIEngine.executeOnText (node_modules/eslint/lib/cli-engine/cli-engine.js:917:26)
      at ESLint.lintText (node_modules/eslint/lib/eslint/eslint.js:593:23)
      at Object.lintText (tests/lib/rules-preprocessor/gjs-gts-processor-test.js:278:34)