The lexer is able to skip leading trivia in the `start` location of tokens.
This makes the source-span more friendly since things like elements
appear to begin at the start of the opening tag, rather than at the
start of any leading whitespace, which could include newlines.
But some tooling requires the full source-span to be available, such
as when tokenizing a text span into an Angular expression.
This commit simply adds the `fullStart` location to the `ParseSourceSpan`
class, and ensures that places where such spans are cloned, this
property flows through too.
PR Close#39486
8d90c1ad97