Allow newlines in single quotes when parsing string nodes

[a-morales]

Description of changes:

Given the valid smithy definition below

@documentation(
"A multiline
documentation
string using
single quotes"
)
structure Foo {}

The LSP parsing code for string nodes was only parsing to the end of the first line. This resulted in subsequent Nodes being incorrect and would result in a NPE here

smithy-language-server/src/main/java/software/amazon/smithy/lsp/language/DocumentSymbolHandler.java

Line 49 in 8dc6c7b

addMemberSymbols(listIterator, symbol);

The Smithy IDL grammar does allow for single quoted strings to contain new lines

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