Support Line decoration for Math [1/2] : Support Highlight for inline and block math equations

[LuxxxLucy]

This is the first of two PR for solving #2200

Regarding #2200, it turns out the highlight is supported for normal text but not for math equations. Digging into it, there are two aspect of it:

1. For block math equations, we just get the frame and then add line based decorations to it.
2. For inline math equations, this becomes a little bit tricky: we have a list of MathParItem consisting of actual Frame or Space, we will need to compute the smallest box that covers the list of all MathParItems.

Note 1
for line based decorations, highlight is a rectangle added to the background of the targeted frame (be it normal text or math equations), so we "prepend" it (adding it beneath the frame), but for other line based decorations, it is **ON TOP OF" the targeted frame. It becomes kind of tricky and thus will be tackled in a next PR

Note 2
A new decoration function is introduced in this PR; the end goal is to merge the new one with the exiting old one. Such refactoring will be included in next PR.

Scope

what is in this MR:

1. support of highlight over inline math equations
2. support of highlight over block math equations
3. corresponding test typ/png

what is not in this MR:

1. support of other line-based decorations.

What will be in the second PR

1. support of other line based decorations.
2. refactor the old "decorate" function and the newly added function introduced in this MR,

[laurmaedje]

Reviewing this as a single PR is easier for me, so I'll review and proceed with #3953 instead.

[LuxxxLucy]

Closing in favour of #3953