Update heuristics to fallback to TSX language if .tsx file is not XML

[vicasas]

Description

This PR fixes the syntax highlighting issue for .tsx files in the TSX language. Previously, the heuristic required detecting a React import pattern in the code. However, in recent versions of React, importing React is no longer necessary, which often resulted in the file being treated as plain text.

The behavior has now been updated to first check for matches with XML languages. If no match is found, it will assume the file is a TSX.

Closes #7039

Checklist:

• I am fixing a misclassified language
  • I have included a new sample for the misclassified language:
    • Sample source(s):
      • [URL to each sample source, if applicable]
    • Sample license(s):
  • I have included a change to the heuristics to distinguish my language from others using the same extension.

[lildude]

LGTM. Thanks.

Note: this PR will not be merged until close to when the next release is made. See here for more details.