[demangler] Use standard semantics for StringView::substr

The StringView::substr now accepts a substring starting position and its
length instead of previous non-standard `from` & `to` positions.

All uses of two argument StringView::substr are in MicrosoftDemangler
and have 0 as a starting position, so no changes are necessary.

This also fixes a bug where attempting to extract a suffix with substr
(a `to` position equal to size) would return a substring without the
last character.

Fixing the issue should not introduce observable changes in the
demangler, since as currently used, a second argument to
StringView::substr is either: 1) a result of a successful call to
StringView::find and so necessarily smaller than size., or 2) in the
case of Demangler::demangleCharLiteral potentially equal to size, but
with demangler expecting more data to follow later on and failing either
way.

Reviewed By: #libc_abi, ldionne, erik.pilkington

Differential Revision: https://reviews.llvm.org/D100246

0 files changed, 0 insertions, 0 deletions