Feature/logging messagetemplate compat

[tkrafael]

Continuing #79038:

• Added documentation to private static methods, so it makes easier future contributions;
• Added unit testing for [LSG] Objects logging using @ operator in logging source generator attribute #78013
• Renaming methods so they're semantically correct when working with '$' symbols in variables
• using Span when possible
• Small bug during variable validation in parser: (src/libraries/Microsoft.Extensions.Logging.Abstractions/gen/LoggerMessageGenerator.Parser.cs:358 in this commit)

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Issue Details

---

Continuing #79038:

• Added documentation to private static methods, so it makes easier future contributions;
• Added unit testing for [LSG] Objects logging using @ operator in logging source generator attribute #78013
• Renaming methods so they're semantically correct when working with '$' symbols in variables
• using Span when possible
• Small bug during variable validation in parser: (src/libraries/Microsoft.Extensions.Logging.Abstractions/gen/LoggerMessageGenerator.Parser.cs:358 in this commit)

Author:	tkrafael
Assignees:	-
Labels:	area-Extensions-Logging, community-contribution
Milestone:	-

[tarekgh]

@tkrafael can you please resolve the conflict? You need to merge with the previous changes.

[tkrafael]

Are checks failing because my changes? I'm looking at build pipeline and failing builds are related with macos and tvos

[tarekgh]

The failures do not look related to the changes. It shows in other PRs like #80392. Let's wait for the CI to finish and we can try restart these failures.