fix: correct MIME types for SVG and JPEG inline display

[PranavGadge01]

Problem

The tm_mimetypes priority list in TeXmacsJulia.jl contained
two incorrect MIME type strings:

• "image/svg" — not a valid MIME type, should be "image/svg+xml"
• "image/jpg" — not a valid MIME type, should be "image/jpeg"

Because showable(MIME("image/svg"), x) and showable(MIME("image/jpg"), x)
never match any object, SVG and JPEG outputs silently fell through to
text/plain, rendering as raw object descriptions instead of images.

Additionally, no display handler existed for SVG at all.

This can be verified in a plain Julia REPL:

using Plots
p = plot(sin, 0, 2π)

showable(MIME("image/jpg"), p)     # false ← was in list
showable(MIME("image/jpeg"), p)    # true  ← correct

showable(MIME("image/svg"), p)     # false ← was in list
showable(MIME("image/svg+xml"), p) # true  ← correct

Fix

• Correct "image/svg" → "image/svg+xml" in tm_mimetypes
• Correct "image/jpg" → "image/jpeg" in tm_mimetypes
• Add missing display handler for MIME"image/svg+xml"

[PranavGadge01]

@hammerfunctor could u please check...