Fix: snippet escaping for resolved code action edits

[amritamishra01]

Summary

Fixes corruption of unrelated source text when applying resolved snippet-based code actions such as Add throws declaration.

Problem

The Java language server returns snippet edits that may contain:

• literal backslashes (\)
• literal dollar signs ($)
• real snippet placeholders like ${1|...|}

These edits were passed directly into SnippetString, causing VS Code to interpret literal characters as snippet syntax.

This led to issues such as:

• "Escaped\\Test\\Path" becoming "Escaped\Test\Path"
• page$content() becoming page()

Fix

Added escapeSnippetLiterals() before creating SnippetString.

This safely escapes:

• literal backslashes
• $ characters that are not snippet placeholders

while preserving valid placeholders like ${1|ExecutionException,Exception,Throwable|}.

Verification

Tested using the reproducer project from #4314.

Verified that:

• escaped backslashes remain unchanged
• page$content() remains unchanged
• Add throws declaration still updates the method signature correctly

Fixes #4314

[datho7561]

Seems good from my testing. Thanks, Amrita!