[golang/go] x/text/encoding/charmap add support for codepage ibm-273 or ibm-1141

### ROOT CAUSE The issue requests the addition of two IBM EBCDIC code pages (273 and 1141) to the `text/encoding/charmap` package. The current package supports simple character encodings like IBM-437 and Windows-1252, but does not include these specific EBCDIC code pages. The issue provides UCM files from ICU as references, but the `charmap` package does not support UCM files directly. The EBCDIC code pages are not common in the Go ecosystem, and their implementation requires specific byte mappings that are not readily available in the standard library. ### CODE FIX The fix involves adding two new charmaps for IBM-273 and IBM-1141 by defining their respective byte-to-rune and rune-to-byte mappings. However, without access to the exact byte mappings for these code pages, the fix cannot be completed. The following is a conceptual approach to implement the fix, but the actual byte values would need to be obtained from reliable sources (e.g., IBM documentation or ICU data) and incorporated into the `charmap` package. 1. **Define New Charmap Tables**: - Create two new tables for IBM-273 and IBM-1141 using the `charmap` package's `NewFromTables` function. - The tables should map runes to bytes and bytes to runes based on the EBCDIC encoding. Example structure (not executable code): ```go // ibm273Table is the mapping for IBM-273. var ibm273Table = []byte{ /* ... */ } // ibm273RuneTable is the rune-to-byte mapping for IBM-273. var ibm273RuneTable = [...]struct { r rune b byte }{ /* ... */ } ``` 2. **Register the New Charmaps**: - Add the new charmaps to the `charmap` package's registry. Example: ```go func init() { // Register IBM-273 charmap.Register("ibm-273", charmap.NewFromTables(ibm273Table, ibm273RuneTable)) // Register IBM-1141 charmap.Register("ibm-1141", charmap.NewFromTables(ibm1141Table, ibm1141RuneTable)) } ``` 3. **Obtain Exact Byte Mappings**: - The exact byte mappings for IBM-273 and IBM-1141 must be obtained from reliable sources, such as IBM's documentation or the ICU UCM files provided in the issue. - These mappings should replace the placeholder values in the tables above. 4. **Update the Package**: - Add the new tables and registration code to the `charmap` package. However, due to the lack of specific byte mappings in the provided context, the fix cannot be implemented without additional data. The issue should be revisited once the exact mappings are available.