Should fluent support string keys that start with an _underscore?

[samreid]

From phetsims/number-pairs#359, I tried adding underscore to indicate "private, internal use only" strings, but it failed a build since all _ are turned into . in one step.

[samreid]

This patch works around the problem in a shallow way:

Details

Subject: [PATCH] Use selector syntax, see https://github.com/phetsims/circuit-construction-kit-common/issues/1039
---
Index: js/grunt/getStringMap.ts
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
diff --git a/js/grunt/getStringMap.ts b/js/grunt/getStringMap.ts
--- a/js/grunt/getStringMap.ts	(revision d40dd51b7421f311de51a3843c1d197cc50a9492)
+++ b/js/grunt/getStringMap.ts	(date 1762561892357)
@@ -256,8 +256,11 @@
 
           // Convert the fluent key back to its JSON style, replacing underscores with dots. Add a leading dot back to match the
           // format of the stringAccesses.
-          const jsonFormattedReference = ( '.' + reference ).replace( /_/g, '.' );
+          let jsonFormattedReference = ( '.' + reference ).replace( /_/g, '.' );
+          jsonFormattedReference = jsonFormattedReference.split( '..' ).join( '._' ); // Handle cases where .. appears due to underscores
+
           if ( !stringAccesses.includes( jsonFormattedReference ) ) {
+            console.log( reference, jsonFormattedReference );
             stringAccesses.push( jsonFormattedReference );
           }
         } );

[samreid]

It looks like we can use a lookup table instead of regex, so I tested with an underscored string. @jessegreenberg can you please review and close if ok?

[samreid]

During phetsims/number-pairs#361 I saw that underscored strings are getting converted to uppercase, which seemed buggy in studio:

      correctAnswerOnFirstTry:
        select_levelType:
          sum:           Correct! { $leftAddend } plus { $rightAddend } equals { $total }. { a11y.gameScreen.responses._correctAnswerScore }
          decomposition: Correct! { $total } can be decomposed into { $leftAddend } and { $rightAddend }. { a11y.gameScreen.responses._correctAnswerScore }
      _correctAnswerScore: |-
                           { $score ->
                             [ 1 ] 1 star!
                             *[ other ] { $score } stars!

outputs:

Is this just one more thing to fix, or a reason to abandon this idea?