[LowieDelneste]

Summary
This PR adds support for generating format-aware overloads for localizer members when a resource contains placeholders such as {0} or {1}.

Changes

• Updated localizer generation to emit parameterized methods when GenerateFormatMethods is enabled.
• Adjusted the generated API so format-based resources produce overloads like HiUser(object arg0) instead of the previous property-plus-overload pattern.
• Exposed the GenerateFormatMethods option through the build props so it can be configured from project metadata.
• Added and updated tests to cover the new behavior.
• Documented the option in the README and quick-start guide.

Why
This makes generated localizers more useful for string formatting scenarios and avoids generating redundant members for format-based resources.

Notes
The behavior is opt-in and controlled by the GenerateFormatMethods setting.

[Dresel]

We use this together with #15 in a local build, and it works well for us. There are two cases where the generated code doesn't fit the text. A fix with tests is on Dresel/ResXGenerator format-methods-fixes, one commit on top of this PR.

1. A placeholder with a format, such as {0:g} or {0,-10}, isn't detected.
<value>Last seen {0:g}</value> gets no method, only the property LastSeen, so the caller has to format the text by hand.

2. A text whose placeholders skip an index gets a method that throws.
<value>Moved {1} to {2}</value>, for example after {0} was removed from the English text while translations still use it, generates

public string Moved(object arg1, object arg2) => stringLocalizer["Moved", arg1, arg2];

string.Format receives two arguments, which fill {0} and {1}, and has nothing for {2}, so the call throws a FormatException. The fix generates a parameter for every index up to the highest, Moved(object arg0, object arg1, object arg2), and arg0 simply goes unused. A build warning for skipped indices would be an alternative.

The fix also ignores escaped braces: {{0}} is literal text and no longer gets a parameter.

One more thing: the README says the option generates "both the existing property-style accessor and a parameterized overload". It generates only the method, since a property and a method can't share a name.