Multi-line expression bodies (ExpressionBodyFactory / AccessorKind.Expression) lose indentation on every line after the first #112

What's wrong

PropertyTemplate (CodeBlocker/Templates/PropertyTemplate.cs:56, ExpressionBodyFactory) and AccessorTemplate (CodeBlocker/Templates/AccessorTemplate.cs:95, AccessorKind.Expression) render the expression fragment and pass it to codeBlocker.Write(...) as one string.

IndentedTextWriter only indents at the start of a Write/WriteLine call, not after newlines embedded in the string. So every continuation line of the fragment lands at the fragment's own indent, not the enclosing one.

TemplateRendering.SpliceFragment was introduced to fix exactly this ("a nested body used to come out flush against the left margin"). It is applied to WriteBody and to block accessors, but not to these two expression paths.

Reproduction (ran)

A ClassTemplate C containing PropertyTemplate public int X, whose ExpressionBodyFactory writes a switch expression:

k switch
{
	_ => 0,
}

• Actual: \tpublic int X => k switch\n{\n\t_ => 0,\n}; (the brace and the arm are one level too shallow).
• Expected: \tpublic int X => k switch\n\t{\n\t\t_ => 0,\n\t};

If the factory ends with WriteLine, the trailing ; also ends up alone on its own line.

Why it matters

Switch expressions, collection expressions and object initializers are the typical multi-line expression bodies, and they all come out mis-indented. That breaks golden-file tests and any consumer that formats or diffs the generated code.

Suggested fix / acceptance criteria

• Split the fragment with TemplateRendering.SplitLines.
• Write the first line inline after =>.
• Emit the remaining lines through the same path SpliceFragment uses so they pick up the current indent.
• Append ; to the last line, not to a trailing empty line.
• Add tests for a nested multi-line expression-bodied property and accessor.