Support image based pdfs in Leo

[rebron]

Description

Some pdfs include text that's not accessible since they're image based.
Leo is not able to summarize or understand these types of pdf docs.

Related: https://chromium-review.googlesource.com/c/chromium/src/+/5246898

Steps to Reproduce

1. View a pdf file e.g. https://www.vintage-trek.com/Trek-Fisher-Klein-Lemond/2004trek.pdf
2. Open Leo
3. Select Summarize and notice content is not applicable to the pdf file.

Actual result:

Expected result:

Leo has access to the text of the pdf document.

Reproduces how often:

Easily.

Brave version (brave://version info)

Version/Channel Information:

• Can you reproduce this issue with the current release? yes
• Can you reproduce this issue with the beta channel? yes
• Can you reproduce this issue with the nightly channel? yes

Other Additional Information:

• Does the issue resolve itself when disabling Brave Shields? n/a
• Does the issue resolve itself when disabling Brave Rewards? n/a
• Is the issue reproducible on the latest version of Chrome? n/a

Miscellaneous Information:

[stephendonner]

Verified PASSED using

Brave | 1.67.73 Chromium: 125.0.6422.26 (Official Build) nightly (64-bit)
-- | --
Revision | 76e7d97680074902ad7bde84f0a1a6c392a4ca6a
OS | Windows 10 Version 22H2 (Build 19045.4355)

example	example

[stephendonner]

Verification PASSED using

Brave | 1.67.73 Chromium: 125.0.6422.26 (Official Build) nightly (x86_64)
-- | --
Revision | 76e7d97680074902ad7bde84f0a1a6c392a4ca6a
OS | macOS Version 11.7.10 (Build 20G1427)

Steps:

1. installed
2. launched Brave
3. loaded https://www.vintage-trek.com/Trek-Fisher-Klein-Lemond/2004trek.pdf
4. clicked on Leo in the sidebar
5. clicked Summarize this page
6. clicked I understand

example	example	example