fix: Fixed all OOB accesses in VertexProgram and PixelProgram

[miniak]

Description of Change

Backport fixes for:

• https://bugs.chromium.org/p/chromium/issues/detail?id=915197
• https://bugs.chromium.org/p/chromium/issues/detail?id=915206
• https://bugs.chromium.org/p/chromium/issues/detail?id=915218

https://swiftshader.googlesource.com/SwiftShader.git/+/0e6a044dff9facf499739be93536bd7f7cc4c6bf

Fix undefined behavior in OFFSET().

Accessing members of a null pointer is undefined behavior, even when
only used to obtain the address again. So use a non-zero value as the
base pointer address instead. 32 was chosen to provide sufficient
alignment guarantees.

https://swiftshader.googlesource.com/SwiftShader.git/+/48d47a4912684bfa4d23d3cdaab60046bf3d0468

Fixed all OOB accesses in VertexProgram and PixelProgram

A lot of arrays in VertexProgram and PixelProgram have fixed sizes,
so programs that have more nested loops or ifs or deeper call stacks
can cause OOB accesses, which causes security issues in Chromium.

Index clamping was added to prevent any OOB memory accesses here.

This could eventually be fixed properly by first verifying these sizes
and giving shader compile errors when these limits are exceeded.

/cc @electron/wg-security

Checklist

• PR description included and stakeholders cc'd
• npm test passes
• PR title follows semantic commit guidelines
• PR release notes describe the change in a way relevant to app developers, and are capitalized, punctuated, and past tense.

Release Notes

Notes: Backported fix for: https://bugs.chromium.org/p/chromium/issues/detail?id=915197, https://bugs.chromium.org/p/chromium/issues/detail?id=915206 and https://bugs.chromium.org/p/chromium/issues/detail?id=915218.

[deepak1556]

Marking it for fixing the compilation errors.

[miniak]

@deepak1556 I've fixed the build error

[release-clerk]

Release Notes Persisted

Backported fix for: https://bugs.chromium.org/p/chromium/issues/detail?id=915197, https://bugs.chromium.org/p/chromium/issues/detail?id=915206 and https://bugs.chromium.org/p/chromium/issues/detail?id=915218.