Fix handling of "\" escape character in identifier names

[poorna2152]

Purpose

Describe the problems, issues, or needs driving this feature/fix and include links to related issues.

Fixes #41507
Fixes #41635

Approach

Describe how you are implementing the solutions along with the design details.

Samples

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Remarks

Note that unescaping more than once would break the code for some scenarios.
e.g. consider: a\\3. (Here user intends to escape the backslash using backslash)
After first unescape: a\3 (Correct)
After second unescape a3 (Wrong)
After third unescape a3 (Wrong)

Check List

• Read the Contributing Guide
• Updated Change Log
• Checked Tooling Support (#)
• Added necessary tests
  • Unit Tests
  • Spec Conformance Tests
  • Integration Tests
  • Ballerina By Example Tests
• Increased Test Coverage
• Added necessary documentation
  • API documentation
  • Module documentation in Module.md files
  • Ballerina By Examples

[codecov]

Codecov Report

Attention: Patch coverage is 98.21429% with 1 line in your changes missing coverage. Please review.

Please upload report for BASE (identifier_unescaping@3dadeb5). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
...lang/compiler/semantics/analyzer/CodeAnalyzer.java	83.33%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@                   Coverage Diff                    @@
##             identifier_unescaping   #41540   +/-   ##
========================================================
  Coverage                         ?   77.51%           
  Complexity                       ?    58584           
========================================================
  Files                            ?     3438           
  Lines                            ?   219217           
  Branches                         ?    28922           
========================================================
  Hits                             ?   169917           
  Misses                           ?    39886           
  Partials                         ?     9414           

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